1. Field of the Invention
The present invention concerns antitumor compounds. More particularly, the invention provides novel taxane derivatives, pharmaceutical compositions thereof, and their use as antitumor agents.
2. Background Art
Taxol(copyright) (paclitaxel) is a natural product extracted from the bark of Pacific yew trees, Taxus brevifolia. It has been shown to have excellent antitumor activity in in vivo animal models, and recent studies have elucidated its unique mode of action, which involves abnormal polymerization of tubulin and disruption of mitosis. It was recently approved for the treatment of ovarian cancer; and studies involving breast, colon, and lung cancers have shown promising results. The results of paclitaxel clinical studies are reviewed in Rowinsky and Donehower, xe2x80x9cThe Clinical Pharmacology and Use of Antimicrotubule Agents in Cancer Chemotherapeuticsxe2x80x9d Pharmac. Ther., 52:35-84, 1991.
Recently, a semi-synthetic analog of paclitaxel named Taxotere(copyright) has also been found to have good antitumor activity in animal models. Taxotere(copyright) is also currently undergoing clinical trials in Europe and the United States. The structures of paclitaxel and Taxotere(copyright) are shown below; the conventional numbering system of the paclitaxel molecule is provided. 
One drawback of paclitaxel is its very limited water solubility requiring it to be formulated in nonaqueous pharmaceutical vehicles. One commonly used carrier is Cremophor EL which may itself have undesirable side effects in man. Accordingly, a number of research teams have prepared water-soluble derivatives of paclitaxel which are disclosed in the following references:
(a) Haugwitz et al, U.S. Pat. No. 4,942,184;
(b) Kingston et al, U.S. Pat. No. 5,059,699;
(c) Stella et al, U.S. Pat. No. 4,960,790;
(d) European Patent Application 0,558,959 A1 published Sep. 8, 1993;
(e) Vyas et al, Bioorganic and Medicinal Chemistry Letters, 1993, 3:1357-1360; and
(f) Nicolaou et al, Nature, 1993, 364:464-466
Compounds of the present invention are phosphonooxymethyl ethers of taxane derivatives and pharmaceutically acceptable salts thereof. The water solubility of the salts facilitates preparation of pharmaceutical formulations.
The present invention relates to taxane derivatives having the formula (A):
Txe2x80x94[OCH2(OCH2)mOP(O)(OH)2]n xe2x80x83xe2x80x83(A) 
wherein T is a taxane moiety bearing on the C13 carbon atom a substituted 3-amino-2-hydroxypropanoyloxy group; n is 1, 2 or 3; m is 0 or an integer from 1 to 6 inclusive; or a pharmaceutically acceptable salt thereof.
Another aspect of the present invention provides taxane derivatives having the formula (B):
Txe2x80x2xe2x80x94[OCH2(OCH2)mSCH3]n xe2x80x83xe2x80x83(B) 
wherein Txe2x80x2 is T in which non-reacting hydroxy groups have been blocked, m and n are as defined under formula (A).
Yet another aspect of the present invention provides intermediates having the formula (C):
Txe2x80x2xe2x80x94[OCH2(OCH2)mOP(O)(ORy)2]n xe2x80x83xe2x80x83(C) 
wherein Txe2x80x2, m and n are as defined under formula (A), and Ry is a phosphono protecting group.
Another aspect of the present invention provides compounds of the formula (D):
13xe2x80x94OHxe2x80x94txnxe2x80x94[OCH2(OCH2)mSCH3]n xe2x80x83xe2x80x83(D) 
wherein m and n are as defined above; and txn is a taxane moiety; or a C13 metal alkoxide thereof.
Another aspect of the present invention provides a method for inhibiting tumor in a mammalian host which comprises administering to said mammalian host an antitumor effective amount of a compound of formula (A).
Further aspect of the present invention provides a method for inhibiting tumor in a mammalian host which comprises administering to said mammalian host an antitumor effective amount of a compound of the formula (Bxe2x80x2): 
wherein R1bxe2x80x2 is hydroxy, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; R3bxe2x80x2 is hydrogen, hydroxy, xe2x80x94OC(O)ORx, C1-6alkyloxy or xe2x80x94OC(O)Rx; one of R6bxe2x80x2 or R7bxe2x80x2 is hydrogen and the other is hydroxy or C1-6 alkanoyloxy; or R6bxe2x80x2 and R7bxe2x80x2 together form an oxo group; R4 and R5 are independently C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, or xe2x80x94Zxe2x80x94R6; Z is a direct bond, C1-6 alkyl or C2-6 alkenyl; R6 is aryl, substituted aryl, C3-6 cycloalkyl or heteroaryl; p is 0 or 1; Rx is C1-6 alkyl optionally, substituted with one to six same or different halogen atoms, C3-6 cycloalkyl, C2-6 alkenyl or hydroxy; or Rx is a radical of the formula 
wherein D is a bond or C1-6 alkyl; and Ra, Rb and Rc are independently hydrogen, amino, C1-6 alkylamino, di-C1-6alkylamino, halogen, C1-6 alkyl, or C1-6 alkoxy.
Thus, another aspect of the present invention provides a pharmaceutical composition which comprises an antitumor effective amount of a compound of formula (Bxe2x80x2) or (A) and a pharmaceutically acceptable carrier.
In the application, unless otherwise specified explicitly or in context, the following definitions apply. xe2x80x9cAlkylxe2x80x9d means a straight or branched saturated carbon chain having from one to six carbon atoms; examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, t-butyl, n-pentyl, sec-pentyl, isopentyl, and n-hexyl. xe2x80x9cAlkenylxe2x80x9d means a straight or branched carbon chain having at least one carbon-carbon double bond, and having from two to six carbon atoms; examples include ethenyl, propenyl, isopropenyl, butenyl, isobutenyl, pentenyl, and hexenyl. xe2x80x9cAlkynylxe2x80x9d means a straight or branched carbon chain having at least one carbon-carbon triple bond, and from two to six carbon atoms; examples include ethynyl, propynyl, butynyl, and hexynyl.
xe2x80x9cArylxe2x80x9d means aromatic hydrocarbon having from six to ten carbon atoms; examples include phenyl and naphthyl. xe2x80x9cSubstituted arylxe2x80x9d means aryl substituted with at least one group selected from C1-6 alkanoyloxy, hydroxy, halogen, C1-6 alkyl, trifluoromethyl, C1-6 alkoxy, aryl, C2-6 alkenyl, C1-6 alkanoyl, nitro, amino, and amido. xe2x80x9cHalogenxe2x80x9d means fluorine, chlorine, bromine, and iodine.
xe2x80x9cPhosphono-xe2x80x9d means the group xe2x80x94P(O) (OH)2 and xe2x80x9cphosphonooxymethoxyxe2x80x9d or xe2x80x9cphosphonooxymethyl etherxe2x80x9d means generically the group xe2x80x94OCH2(OCH2)mOP(O) (OH)2. xe2x80x9c(Methylthio)thiocarbonylxe2x80x9d means the group xe2x80x94C(S)SCH3. xe2x80x9cMethylthiomethylxe2x80x9d (also abbreviated as MTM) generically refers to the group xe2x80x94CH2SCH3.
xe2x80x9cTaxane moietyxe2x80x9d (also abbreviated as txn) denotes moieties containing the twenty carbon taxane core framework represented by the structural formula shown below with the absolute configuration. 
The numbering system shown above is one used in conventional taxane nomenclature, and is followed throughout the application. For example, the notation C1 refers to the carbon atom labelled as xe2x80x9c1xe2x80x9d; C5-C20 oxetane refers to an oxetane ring formed by the carbon atoms labelled as 4, 5 and 20 with an oxygen atom; and C9 oxy refers to an oxygen atom attached to the carbon atom labelled as xe2x80x9c9xe2x80x9d, said oxygen atom may be an oxo group, xcex1- or xcex2-hydroxy, or xcex1- or xcex2-acyloxy.
xe2x80x9cSubstituted 3-amino-2-hydroxypropanoyloxyxe2x80x9d denotes a residue represented by the formula 
(X is a nonhydrogen group and Xxe2x80x2 is hydrogen or a non-hydrogen group.) The stereochemistry of this residue is the same as the paclitaxel sidechain. This group is sometimes referred to in the application as the xe2x80x9cC13 sidechain.xe2x80x9d
xe2x80x9cTaxane derivativexe2x80x9d (abbreviated as T) refers to a compound having a taxane moiety bearing a C13 sidechain.
xe2x80x9cHeteroarylxe2x80x9d means a five- or six-membered aromatic ring containing at least one and up to four non-carbon atoms selected from oxygen, sulfur and nitrogen. Examples of heteroaryl include thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, triazolyl, thiadiazolyl, oxadiazolyl, tetrazolyl, thiatriazolyl, oxatriazolyl, pyridyl, pyrimidyl, pyrazinyl, pyridazinyl, triazinyl, tetrazinyl, and like rings.
xe2x80x9cPhosphono protecting groupsxe2x80x9d means moieties which can be employed to block or protect the phosphono functional group; preferably such protecting groups are those that can be removed by methods that do not appreciably affect the rest of the molecule. Suitable phosphonooxy protecting groups are well known to those skilled in the art and include for example benzyl and allyl groups.
xe2x80x9cHydroxy protecting groupsxe2x80x9d include, but is not limited to, ethers such as methyl, t-butyl, benzyl, p-methoxybenzyl, p-nitrobenzyl, allyl, trityl, methoxymethyl, methoxyethoxymethyl, ethoxyethyl, tetrahydropyranyl, tetrahydrothiopyranyl, and trialkylsilyl ethers such as trimethylsilyl ether, triethylsilyl ether, and t-butyldimethylsilyl ether; esters such as benzoyl, acetyl, phenylacetyl, formyl, mono-, di-, and trihaloacetyl such as chloroacetyl, dichloroacetyl, trichloroacetyl, trifluoroacetyl; and carbonates such as methyl, ethyl, 2,2,2-trichloroethyl, allyl, benzyl, and p-nitrophenyl.
Additional examples of hydroxy and phosphono protecting groups may be found in standard reference works such as Greene and Wuts, Protective Groups in Organic Synthesis, 2d Ed., 1991, John Wiley and Sons, and McOmie, Protective Groups in Organic Chemistry, 1975, Plenum Press. Methods for introducing and removing protecting groups are also found in such textbooks.
xe2x80x9cPharmaceutically acceptable saltxe2x80x9d means a metal or an amine salt of the acidic phosphono group in which the cation does not contribute significantly to the toxicity or biological activity of the active compound. Suitable metal salts include lithium, sodium, potassium, calcium, barium, magnesium, zinc, and aluminum salts. Preferred metal salts are sodium and potassium salts. Suitable amine salts are for example, ammonia, tromethamine (TRIS), triethylamine, procaine, benzathine, dibenzylamine, chloroprocaine, choline, diethanolamine, triethanolamine, ethylenediamine, glucamine, N-methylglucamine, lysine, arginine, ethanolamine, to name but a few. Preferred amine salts are lysine, arginine, triethanolamine, and N-methylglucamine salts. Even more preferred salt is N-methylglucamine or triethanolamine.
As used herein, the term xe2x80x94OCH2(OCH2)mOP(O)(OH)2 is intended to emcompass both the free acid and its pharmaceutically acceptable salts, unless the context indicates specifically that the free acid is meant.
One aspect of the present invention provides taxane derivatives of the formula (A)
Txe2x80x94[OCH2(OCH2)mOP(O)(OH)2]n xe2x80x83xe2x80x83(A) 
wherein T is a taxane moiety bearing on the C13 carbon atom a substituted 3-amino-2-hydroxypropanoyloxy group; n is an 1, 2 or 3; m is 0, or an integer from 1 to 6 inclusive, or a pharmaceutically acceptable salt thereof.
Another aspect of the present invention provides taxane derivatives having the formula (B)
Txe2x80x2xe2x80x94[OCH2(OCH2)mSCH3]n xe2x80x83xe2x80x83(B) 
which are useful in making taxane derivatives of the formula (A).
In one embodiment the taxane moiety contains at least the following functionalities: C1-hydroxy, C2-benzoyloxy, C4-acetyloxy, C5-C20 oxetane, C9-oxy, and C11-C12 double bond.
In a preferred embodiment the taxane moiety is derived from a residue having the formula 
wherein R2exe2x80x2 is hydrogen and R2e is hydrogen, hydroxy, xe2x80x94OC(O)Rx, or xe2x80x94OC(O)ORx; or R2e is hydrogen and R2exe2x80x2 is fluoro; R3e is hydrogen, hydroxy, xe2x80x94OC(O)Rx, xe2x80x94OC(O)ORx or C1-6alkyloxy; one of R6e or R7e is hydrogen and the other is hydroxy or xe2x80x94OC(O)Rx; or R6e and R7e together form an oxo group; Rx is as defined below.
In another embodiment, the C13 sidechain is derived from a residue having the formula 
wherein R1e is hydrogen or xe2x80x94C(O)Rx, xe2x80x94C(O)ORx; R4 and R5 are independently C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, or xe2x80x94Zxe2x80x94R6; Z is a direct bond, C1-6 alkyl or C2-6 alkenyl; R6 is aryl, substituted aryl, C3-6 cycloalkyl, or heteroaryl; and Rx is C1-6 alkyl optionally substituted with one to six same or different halogen atoms, C3-6 cycloalkyl, C2-6 alkenyl or hydroxy; or Rx is a radical of the formula 
wherein D is a bond or C1-6 alkyl; and Ra, Rb and Rc are independently hydrogen, amino, C1-6 alkylamino, di-C1-6 alkylamino, halogen, C1-6 alkyl, or C1-6 alkoxy; p is 0 or 1.
In a preferred embodiment, R4 is C1-6 alkyl and p is 1, or R4 is or xe2x80x94Zxe2x80x94R6 and p is 0. More preferably, R4(O)p is t-butoxy, phenyl, isopropyloxy, n-propyloxy, or n-butoxy.
In another preferred embodiment R5 is C2-6alkenyl or xe2x80x94Zxe2x80x94R6 and Z and R6 are as previously defined. More preferably, R5 is phenyl, 2-furyl, 2-thienyl, isobutenyl, 2-propenyl, or C3-6cycloalkyl.
In another embodiment, compound of formula (A) may be more specifically represented by the formula (I) 
wherein R1 is hydroxy, xe2x80x94OCH2(OCH2)mOP(O)(OH)2, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; R2 is hydrogen, and R2 is hydrogen, hydroxy, xe2x80x94OCH2(OCH2)mOP(O)(OH)2 or xe2x80x94OC(O)ORx; or R2xe2x80x2 is fluoro, and R2 is hydrogen; R3 is hydrogen, hydroxy, C1-6alkyloxy, xe2x80x94OC(O)Rx, xe2x80x94OCH2(OCH2)mOP(O)(OH)2 or xe2x80x94OC(O)ORx; one of R6 or R7 is hydrogen and the other is hydroxy, C1-6 alkanoyloxy, or xe2x80x94OCH2(OCH2)mOP(O)(OH)2; or R6 and R7 together form an oxo group; with the proviso that at least one of R1, R2, R3, R6 or R7 is xe2x80x94OCH2(OCH2)mOP(O)(OH)2; R4, R5, Rx, m and p are as previously defined; or a pharmaceutically acceptable salt thereof.
In compounds of formula (I), examples of Rx include methyl, hydroxymethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, chloromethyl, 2,2,2-trichloroethyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, ethenyl, 2-propenyl, phenyl, benzyl, bromophenyl, 4-aminophenyl, 4-methylaminophenyl, 4-methylphenyl, 4-methoxyphenyl and the like. Examples of R4 and R5 include 2-propenyl, isobutenyl, 3-furanyl (3-furyl), 3-thienyl, phenyl, naphthyl, 4-hydroxyphenyl, 4-methoxyphenyl, 4-fluorophenyl, 4-trifluoromethylphenyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, ethenyl, 2-propenyl, 2-propynyl, benzyl, phenethyl, phenylethenyl, 3,4-dimethoxyphenyl, 2-furanyl (2-furyl), 2-thienyl, 2-(2-furanyl)ethenyl, 2-methylpropyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexylmethyl, cyclohexylethyl and the like.
In one embodiment, the present invention provides a preferred group of compounds of formula (I) in which R5 is C2-6alkenyl or xe2x80x94Zxe2x80x94R6 and Z and R6 are as previously defined. More preferably, R5 is phenyl, 3-furyl, 3-thienyl, 2-propenyl, isobutenyl, 2-furyl, 2-thienyl, or C3-6cycloalkyl.
In another preferred embodiment R4 of compounds of formula (I) is C1-6alkyl in which case p is 1; or R4 is xe2x80x94Zxe2x80x94R6 and Z and R6 are as previously defined, and in which case p is 0. More preferably R4(O)pxe2x80x94 is t-butoxy, phenyl, isopropyloxy, n-propyloxy, n-butoxy.
In another preferred embodiment, the present invention provides compounds of formula (I) in which R1 is xe2x80x94OCH2(OCH2)mOP(O)(OH)2. In a more preferred embodiment, R2 is hydroxy, xe2x80x94OCH2(OCH2)mOP(O)(OH)2, or xe2x80x94OC(O)Rx, and Rx is preferably C1-6 alkyl. In another more preferred embodiment, R3 is hydroxy or acetoxy.
In another preferred embodiment, the present invention provides compound of formula (I) in which R2 is xe2x80x94OCH2(OCH2)mOP(O)(OH)2; R1 is hydroxy or xe2x80x94OC(O)ORx; and R3 is hydrogen, hydroxy, acetoxy, xe2x80x94OCH2(OCH2)mOP(O)(OH)2 or xe2x80x94OC(O)ORx; and Rx is as previously defined. In a more preferred embodiment R1 is hydroxy or xe2x80x94OC(O)ORx and Rx is preferably C1-6 alkyl; and R3 is hydroxy or acetoxy.
In another preferred embodiment, the present invention provides compound of formula (I) in which R3 is xe2x80x94OCH2(OCH2)mOP(O)(OH)2; R1 is hydroxy or xe2x80x94OC(O)ORx; R2xe2x80x2 is hydrogen, and R2 is hydrogen, hydroxy or xe2x80x94OC(O)ORx; or R2xe2x80x2 is fluoro and R2 is hydrogen; and Rx is as previously defined. In a more preferred embodiment, R1 is hydroxy or xe2x80x94OC(O)ORx, and Rx is preferably C1-6 alkyl. In another more preferred embodiment, R2 is hydroxy.
In another preferred embodiment, m is 0 or 1 when the phosphonooxymethoxy group is present on the C7 of the taxane moiety.
The preferred pharmaceutically acceptable salts of a compound of formula (A) are alkali metal salts including lithium, sodium and potassium salts; and amine salts including triethylamine, triethanolamine, ethanolamine, arginine, lysine and N-methylglucamine salts. Even more preferred salts are sodium, triethanolamine, and N-methylglucamine salts.
The most preferred embodiments of taxane derivatives of formula (A) include the following compounds: (1) 7-O-phosphonooxymethylpaclitaxel, (2) 2xe2x80x2-O-(ethyloxycarbonyl)-7-O-phosphonooxymethylpaclitaxel; (3) 2xe2x80x2-O-phosphonooxymethylpaclitaxel; (4) 2xe2x80x2,7-bis-O-(phosphonooxymethyl)paclitaxel; (5) 3xe2x80x2-N-debenzoyl-3xe2x80x2-desphenyl-3xe2x80x2-N-(t-butyloxycarbonyl)-3xe2x80x2-(2-furyl)-2xe2x80x2-O-ethyloxycarbonyl-7-O-phosphonooxymethylpaclitaxel; (6) 3xe2x80x2-N-debenzoyl-3xe2x80x2-desphenyl-3xe2x80x2-N-(t-butyloxycarbonyl)-3xe2x80x2-(2xe2x80x2-thienyl)-2-O-ethyloxycarbonyl-7-O-phosphonooxymethylpaclitaxel; (7) 10-desacetyl-3xe2x80x2-N-desbenzoyl-3xe2x80x2-N-(t-butyloxycarbonyl)-10-O-(phosphonooxymethyl)paclitaxel; (8) 2xe2x80x2-O-phosphonooxymethoxymethylpaclitaxel; (9) 2xe2x80x2-O-n-propylcarbonyl-7-O-phosphonooxymethylpaclitaxel; (10) 2xe2x80x2-O-methylcarbonyl-7-O-phosphonooxymethylpaclitaxel; (11) 2xe2x80x2-O-methoxycarbonyl-7-O-phosphonooxymethylpaclitaxel; (12) 2xe2x80x2-O-phosphonooxymethoxymethyl-7-O-phosphonooxymethylpaclitaxel; and their respective pharmaceutically acceptable salts, particularly the sodium, potassium, arginine, lysine, N-methylglucamine, ethanolamine, triethylamine and triethanolamine salts.
Compounds of formula (A) may be prepared from a taxane derivative starting material T-[OH]n wherein T and n are as previously defined. The identity of T-[OH]n is not particularly limited so long as there is at least one reactive hydroxy group present on either the taxane moiety or the C13 side chain to allow the formation of phosphonooxymethyl ether linkage. It is to be understood that the reactive hydroxy group may be directly attached to the C13 propanoyloxy backbone (e.g. the 2xe2x80x2-hydroxy group of paclitaxel) or to the taxane core framework (e.g. the 7-hydroxy group of paclitaxel); or it may be present on a substituent on the C13 sidechain, or on a substituent on the taxane core. The reaction sequence shown in Scheme I may be used to prepare compounds of formula (A) 
In Scheme I Txe2x80x2 is a taxane derivative in which non-reacting hydroxy groups have been blocked; Ry is a phosphono protecting group; n and m are as previously defined. Thus an appropriately protected Txe2x80x2 having one or more reactive hydroxy groups is first converted to a corresponding methylthiomethyl ether of formula (B). Using paclitaxel as an example, Txe2x80x2 may be paclitaxel itself (to effect 2xe2x80x2,7-bismethylthiomethylation), 7-O-triethylsilylpaclitaxel, 7-O-benzyloxycarbonylpaclitaxel, or 2xe2x80x2-O-ethoxycarbonylpaclitaxel. A compound of formula (B) where m is 0 may be prepared by treating Txe2x80x2-[OH]n with dimethylsulfoxide/acetic anhydride, or with dimethylsulfide and an organic peroxide. These reactions are discussed more fully in a subsequent section.
The MTM ether having one intervening methyleneoxy unit (i.e. compounds of formula (B) where m=1) may be prepared by several possible routes. In one a compound of formula (B) where m=0 is reacted with N-iodosuccinimide (NIS) and methylthiomethanol to extend the chain by one methyleneoxy unit. 
An analogous reaction of an alcohol with methylthiomethyloxy group in the presence of NIS was reported by Veeneman et al, in Tetrahedron, 1991, v47, pp. 1547-1562, the relevant portions thereof are hereby incorporated by reference. Silver triflate is preferably used as a catalyst.
The compound of methylthiomethanol and its preparation is reported in Syn. Comm., 1986, 16 (13): 1607-1610.
In an alternative method, the T-alkoxide (Ad) generated by treating a compound of formula (Aa) with a base such as n-butyl lithium, lithium diisopropylamide or lithium hexamethyldisilazide, is reacted with chloromethyl methylthiomethyl ether to provide a compound of formula (B) in which m=1. 
Compound (Ae) is prepared by reacting methylthiomethoxide (obtained from methythiomethanol by treatment with a base such as n-butyl lithium, lithium diisopropylamide or lithium hexamethyldisilazide) with chloroiodomethane. Compound (Ae) may also be prepared by treating 1,1xe2x80x2-dichlorodimethylether (ClCH2OCH2Cl) with a stoichiometric amount or less (e.g. about 0.8 equivalent) of sodium iodide followed by sodium thiomethoxide. 1,1xe2x80x2-Dichlorodimethyl ether is reported in Ind. J. Chem., 1989, 28B, pp. 454-456.
In another method, a compound of formula (Aa) is reacted with bis(MTM)ether, CH3SCH2OCH2SCH3, and NIS to give a compound of formula (B) in which m=1.
Txe2x80x2xe2x80x94[OH]n+n CH3SCH2OCH2SCH3xe2x86x92Txe2x80x2xe2x80x94[OCH2OCH2SCH3]n 
Bis(MTM)ether is prepared by reacting 1,1xe2x80x2-dichlorodimethyl ether with sodium iodide followed by sodium thiomethoxide.
The procedure described above using methylthiomethanol and NIS may be applied to any reagent having an MTM group to extend the chain by one methyleneoxy unit at a time. For example, a compound of formula (B) wherein m=1 can be reacted with methythiomethanol and NIS to provide a compound of formula (B) wherein m=2. The process may be repeated to provide compounds of formula (B) in which m is 3, 4, 5 or 6.
In the second step shown in Scheme I, the methylthiomethyl ether is converted to the corresponding protected phosphonooxymethyl ether. This is accomplished by treating the MTM ether with NIS and protected phosphate HOP(O)(ORy)2. In the third step, the phosphono protecting group and any hydroxy protecting group(s) are removed to provide a compound of formula (A). For example, a suitable phosphono protecting group is benzyl which may be removed by catalytic hydrogenolysis; hydroxy protecting groups such as trialkysilyl may be removed by fluoride ion, trichloroethoxycarbonyl may be removed by zinc. Removal of protecting groups are taught in textbooks such as Green and Wuts, Protective Groups in Organic Synthesis, John Wiley and Sons, 1991; and McOmie, Protective in Organic Chemistry, Plenum Press, 1973. Both steps are discussed in detail in a later section in the specification.
A variation of the reaction sequence shown in Scheme I is provided in Scheme II. 
In Scheme II, a compound of formula (Aa) is reacted with a compound of formula (Ca) and NIS to give a compound of formula (C), which is then deblocked to give a compound of formula (A). Compounds of formula (Ca) in which m is 0 may be prepared by first treating methylthiomethanol with a base such as Na, Li or K hexamethyldisilazide to give methylthiomethoxide; the methoxide is then reacted with a protected chlorophosphate such as dibenzyl chlorophosphate to provide the desired-compound. Compounds of formula (Ca) in which m is 1 may be prepared by treating CH3SCH2OCH2Cl with a diprotected phosphate salt, e.g. sodium, potassium, tetra(n-butyl)ammonium salts of dibenzyl phosphate; or CH3SCH2OCH2Cl may be first converted to the corresponding iodo compound using sodium iodide prior to reacting with the phosphate salt. Alternatively, compounds of formula (Ca) in which m is 1 may be prepared by, treating ClCH2OCH2Cl with sodium iodide followed by sodium thiomethoxide to provide CH3SCH2OCH2SCH3; this compound is then treated with NIS and a diprotected phosphate such as dibenzyl phosphate to give the desired product. Any of the previously mentioned reagents having a MTM group may be extended one methyleneoxy unit at a time by reacting said reagent with methylthiomethanol and NIS.
In another method for preparing a compound of formula (A), T-alkoxide (Ad) is reacted with an iodophosphate as shown in Scheme III. 
In Scheme III, the iodophosphate compound is obtained by reacting ClCH2(OCH2)mCl with a diprotected phosphate salt to give ClCH2(OCH2)mOP(O)(ORy)2 which is then treated with sodium iodide to give the desired product.
Yet another method suitable for preparing a subset of compounds of formula (A) in which at least one of the phosphonooxymethoxy groups is linked to the taxane moiety is shown in Scheme IV. 
In Scheme IV, m and n are as previously defined; X is a non-hydrogen group, P is a hydroxy protecting group; txn is a taxane moiety. Compounds of formula (D) are taxanes having a 13xcex1-hydroxy group and one or more methylthiomethyl ether linked directly or indirectly to the taxane core; also included are C13 metal alkoxides of formula (D). An example of a compound of formula (D) is 7-O-methylthiomethylbaccatin III: 
The coupling of the taxane (D) with the azetidinone is analogous to the one shown in Scheme VI, infra; thus the procedure described there for the preparation of a compound of formula (Id) is also applicable to the preparation of a compound of formula (Ba) [i.e. a compound of formula (B) in which at least one of the MTM group is linked directly or indirectly to the taxane moiety], if a compound of formula (D) is used in place of a compound of formula (II) in Scheme VI. The taxane (D) is preferably first converted to a C13 metal alkoxide such as sodium, potassium or lithium alkoxide; lithium alkoxide is preferred. The azetidinone serves as the precursor of the C13 sidechain. After the coupling reaction with a taxane, the hydroxy protecting group P is removed, and if desired, the free hydroxy group on the sidechain may be converted to the MTM ether or derivatized to an ester or a carbonate as herein described.
The azetidinone may be prepared by methods described later which are also methods generally known in the art. Compounds of formula (D) may be prepared by the general procedure described above for the preparation of compounds of formula (B) using a suitably protected taxane. However, more conveniently, they can be obtained from a compound of formula (Ba) by cleaving the 13-sidechain using a borohydride such as sodium or tetrabutylammonium borohydride; for example, 7-O-MTM of paclitaxel is treated with tetrabutylammonium borohydride to give 7-O-MTM baccatin III.
The general process of Scheme I for the preparation of a compound of formula (A) is more particularly exemplified in Scheme V which illustrates the preparation of a compound of formula (Ixe2x80x2) (i.e. a compound of formula (I) in which m is 0). The procedure employed in this synthetic sequence is generally applicable to other taxane derivatives not specifically encompassed by formula (I). Furthermore, the procedure in Scheme (V) may be modified in accordance with teachings contained herein by one skilled in the art to arrive at taxane derivatives of formula (A) in which m is 1, 2 or 3.
It is to be understood that in Scheme V as well as elsewhere in the specification, the term xe2x80x9chydroxy protecting groupxe2x80x9d may encompass suitable carbonates (e.g. xe2x80x94OC(O)ORx in which Rx does not contain hydroxy); thus, when a carbonate is used as a hydroxy protecting group, it is intended to be removed in a later step to generate the free hydroxy group, otherwise, the carbonate moiety remains as part of the final product. 
In Scheme V, R1a is hydroxy, protected hydroxy, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx ; R2 is hydrogen, and R2a is hydrogen, hydroxy, protected hydroxy or xe2x80x94OC(O)ORx; or R2xe2x80x2 is fluoro, and R2a is hydrogen; R3a is hydrogen, hydroxy, protected hydroxy, C1-6alkyloxy, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; one of R6a or R7a is hydrogen and the other is hydroxy, protected hydroxy or C1-6 alkanoyloxy; or R6a and R7a together form an oxo group; with the proviso that at least one of R1a, R2a or R3a, R6a or R7a is hydroxy. R1b is hydroxy, protected hydroxy, xe2x80x94OCH2SCH3, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; R2xe2x80x2 is hydrogen, and R2b is hydrogen, hydroxy, protected hydroxy, xe2x80x94OCH2SCH3 or xe2x80x94OC(O)ORx; or R2xe2x80x2 is fluoro, and R2b is hydrogen; R3b is hydrogen, hydroxy, protected hydroxy, C1-6alkyloxy, xe2x80x94OC(O)Rx, xe2x80x94OCH2SCH3 or xe2x80x94OC(O)ORx; one of R6b or R7b is hydrogen and the other is hydroxy, protected hydroxy, C1-6 alkanoyloxy or xe2x80x94OCH2SCH3; or R6b and R7b together form an oxo group; with the proviso that at least one of R1b, R2b, R3b, R6b or R7b is xe2x80x94OCH2SCH3. R1c is hydroxy, protected hydroxy, xe2x80x94OCH2OP(O)(ORy)2, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; R2 is hydrogen, and R2c is hydrogen, hydroxy, protected hydroxy, xe2x80x94OCH2OP(O)(ORy)2 or xe2x80x94OC(O)ORx; or R2 is fluoro, and R2c is hydrogen; R3c is hydrogen, hydroxy, protected hydroxy, C1-6alkyloxy, xe2x80x94OC(O)Rx, xe2x80x94OCH2OP(O)(ORy)2 or xe2x80x94OC(O)ORx; one of R6c or R7c is hydrogen and the other is hydroxy, protected hydroxy, C1-6 alkanoyloxy or xe2x80x94OCH2OP(O)(ORy)2; with the proviso that at least one of R1c, R2c, R3c, R6c or R7c is xe2x80x94OCH2OP(O)(ORy)2. R1xe2x80x2 is hydroxy, xe2x80x94OCH2OP(O)(OH)2, xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx; R2xe2x80x3xe2x80x2 is hydrogen, and R2xe2x80x3 is hydrogen, hydroxy, xe2x80x94OCH2OP(O)(OH)2 or xe2x80x94OC(O)ORx; or R2xe2x80x2xe2x80x3 is fluoro, and R2xe2x80x3 is hydrogen; R3xe2x80x2 is hydrogen, hydroxy, C1-6alkyloxy, xe2x80x94OC(O)Rx, xe2x80x94OCH2OP(O)(OH)2 or xe2x80x94OC(O)ORx; one of R6xe2x80x2 or R7xe2x80x2 is hydrogen and the other is hydroxy, C1-6 alkanoyloxy or xe2x80x94OCH2OP(O)(OH)2; with the proviso that at least one of R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R6xe2x80x2 or R7xe2x80x2 is xe2x80x94OCH2OP(O)(OH)2. R4, R5, Rx, and p are as defined previously, and Ry is a phosphono protecting group.
In the first step, the free hydroxy group of a compound of formula (Ia) is converted to the corresponding methylthiomethyl ether (xe2x80x94OCH2SCH3) group. This conversion may be accomplished by either one of the two procedures (1axe2x80x94the dimethylsulfide method) and (1bxe2x80x94the dimethylsulfoxide method). The dimethylsulfide method for converting alcohols to methylthiomethyl ethers is reported in Medina et al, Tet. Lett., 1988, pp. 3773-3776, the relevant portions thereof are hereby incorporated by reference. The dimethylsulfoxide method is the well-known reaction commonly known as the Pummerer reaction.
It should be noted that the reactivity of a hydroxy group differs depending on its location on the taxane derivative starting material of formula (Ia). Although in general the 2xe2x80x2-hydroxy group is more reactive in acylation reactions than the 7-hydroxy group which in turn is more reactive than the 10-hydroxy group, it has been found that, surprisingly with the dimethylsulfide method, the 7-hydroxy is more readily converted into the methylthiomethyl ether than the 2xe2x80x2-hydroxy group. The tertiary hydroxy group at C-1 is usually the least reactive. The difference in hydroxy reactivity may be exploited in controlling the site and degree of methylthiomethylation.
Thus with a compound of formula (Ia) wherein R1a and R2a are both hydroxy, the predominant methylthiomethylation product is the corresponding 7-O-methylthiomethyl ether with the dimethylsulfide method. In order to obtain a compound of formula (Ib) wherein R1b is methylthiomethoxy, without also converting the 7-hydroxy group, if present, into a methylthiomethyl ether, the 7-hydroxy group is blocked with a conventional hydroxy protecting group such as triethylsilyl. Similarly, 10-methylthiomethyl ether may be obtained without also converting the 7- and/or 2xe2x80x2-hydroxy groups, if present, when the latter groups are blocked by the same of different hydroxy protecting groups. Even though the 7-hydroxy is the preferential methylthiomethylation site in the dimethylsulfide method, it is still preferable to protect the 2xe2x80x2-hydroxy group if the 7-monomethylthiomethyl ether is the desired product.
Moreover, the reaction conditions may be manipulated to favor the formation of bis- or tris-methylthiomethyl ether taxane derivatives. For example, in the case of paclitaxel, increasing reaction time or using a larger excess of the methylthiomethylating reagents can result in a higher ratio of 2xe2x80x2,7-bis(methylthiomethyl) ether paclitaxel in the product mixture.
Returning now to Scheme V, in procedure (1a) a compound of formula (Ia) is treated with dimethylsulfide and an organic peroxide such as benzoyl peroxide. The reaction is carried out in an inert organic solvent such as acetonitrile, methylene chloride and the like at a temperature conducive to product formation; typically the reaction is carried at a temperature range of from about xe2x88x9240xc2x0 C. to about ambient temperature. Dimethylsulfide and benzoyl peroxide are used in excess relative to the taxane derivative starting material (Ia), and dimethylsulfide is used in excess relative to benzoyl peroxide.
The relative amounts of starting materials used will depend on the degree of methylthiomethylation to be achieved. Thus when one free hydroxy group of the taxane derivative starting material (Ia) is to be converted to the methylthiomethyl ether, dimethylsulfide and benzoyl peroxide may be used in up to 10 fold excess relative to taxane derivative (Ia); and preferably, dimethylsulfide is used in about two to three fold excess relative to benzoyl peroxide. In the case where the starting material (Ia) has both 2xe2x80x2- and 7-hydroxy groups, the amount of 2xe2x80x2,7-bis(methylthiomethyl)ether obtained increases with the relative amounts of dimethylsulfide and benzoyl peroxide. When 2xe2x80x2,7-bis(methylthiomethyl) ether is the desired product, dimethylsulfide is preferably used in about 15 to about 20 fold excess of the taxane derivative starting material; and benzoyl peroxide is used in about 5 to about 10 fold excess relative to the taxane derivative starting material.
Alternatively, a compound of formula (Ib) may be prepared by reacting a compound of formula (Ia) with dimethylsulfoxide and acetic anhydride (procedure 1b). This procedure is suitable for derivatizing a non-2xe2x80x2-hydroxy group into its methylthiomethyl ether. In procedure (1b), a compound of formula (Ia) is dissolved in dimethylsulfoxide and acetic anhydride is added to the solution. The reaction is usually carried out at room temperature, and for 18-24 hours to produce the monomethylthiomethyl ether.
In the second step of the reaction sequence, the methylthiomethyl ether is converted to the corresponding protected phosphonooxymethyl ether. The methylthiomethyl to protected phosphonooxymethyl conversion may be accomplished by the general method reported in Veeneman et al, Tetrahedron, 1991, v47, pp. 1547-1562, the relevant portions thereof are hereby incorporated by reference. Thus, a compound of formula (Ib) with at least one methylthiomethyl ether group is treated with N-iodosuccinimide and a protected phosphoric acid such as dibenzyl phosphate. The reaction is carried out in an inert organic solvent such as tetrahydrofuran or a halogenated hydrocarbon such as 1,2-dichloroethane or methylene chloride, and optionally in the presence of a dehydrating agent such as molecular sieves. A catalyst such as silver trifluoromethanesulfonate may also be added to accelerate the reaction. The reaction is carried out at a temperature ranging from about 0xc2x0 C. to about room temperature, preferably at room temperature. N-Iodosuccinimide and the protected phosphoric acid are used in about the same molar equivalent as the methylthiomethylether (Ib), but preferably they are used in slight excess, for example about 1.3 to about 1.5 equivalents relative to compound of formula (Ib).
In the third step of the reaction sequence, the phosphono protecting group and hydroxy protecting group, if present, are removed. The deblocking is accomplished by conventional methods well known in the art such as acid- or base-catalyzed hydrolysis, hydrogenolysis, reduction, and the like. For example, catalytic hydrogenolysis can be used to remove the benzyl phosphono protecting group as well as the benzyloxycarbonyl hydroxy protecting group. Deprotecting methodologies may be found in standard texts such as Greene and Wutz, or McOmie, supra. Needless to say if a compound of formula (Ia) contains hydroxy groups in radical Rx, said hydroxy groups are preferably protected with suitable hydroxy protecting groups until deprotected in this last step.
As indicated earlier the procedure in Scheme V may be modified in accordance with the teaching contained herein by one skilled in the art to arrive at taxane derivatives of formula A in which m 1, 2 or 3. As examples, Schemes Va and Vb specifically illustrate how one skilled in the art can modify the teaching contained herein to arrive at certain compounds of formula A wherein at least one substitutent is xe2x80x94OCH2OCH2OCH2OP(O)(OH)2. Similarly other compounds of formula A in which m is 2 or 3 can be readily obtaiined. 
The base salts of a compound of formula (I) may be formed by conventional techniques involving contacting a compound of formula (I) free acid with a metal base or with an amine. Suitable metal bases include hydroxides, carbonates and bicarbonates of sodium, potassium, lithium, calcium, barium, magnesium, zinc, and aluminum; and suitable amines include triethylamine, ammonia, lysine, arginine, N-methylglucamine, ethanolamine, procaine, benzathine, dibenzylamine, tromethamine (TRIS), chloroprocaine, choline, diethanolamine, triethanolamine and the like. The base salts may be further purified by chromatography followed by lyophilization or crystallization.
TAXANE DERIVATIVES STARTING MATERIALS
The processes described above may be applied to any taxane derivatives of the formula T-[OH]n to form compounds of formula (A). Many examples of T-[OH]n have been reported in the literature and some of which are listed below. (a) paclitaxel; (b) Taxotere(copyright); (c) 10-desacetylpaclitaxel; (d) taxane derivatives disclosed in PCT application 93/06079 (published Apr. 1, 1993) having the formula 
wherein R1 is xe2x80x94OR6, xe2x80x94SR7, or xe2x80x94NR8R9; R2 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; R3 and R4 are independently hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, or acyl, provided, however, that R3 and R4 are not both acyl; R5 is xe2x80x94COR10, xe2x80x94COOR10, xe2x80x94COSR10, xe2x80x94CONR8R10, xe2x80x94SO2R11, or xe2x80x94POR12R13;R6 is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxy protecting group, or a functional group which increases the water solubility of the taxane derivative; R7 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, or sulfhydryl protecting group; R8 is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl; R9 is an amino protecting group; R10 is alkyl, alkenyl, alkynyl, aryl, heteroaryl; R11 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, xe2x80x94OR10, or xe2x80x94NR8R14; R12 and R13 are independently alkyl, alkenyl, alkynyl, aryl, heteroaryl, xe2x80x94OR10, or xe2x80x94NR8R14; R14 is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl; R15 and R16 are independently hydrogen, hydroxy, lower alkanoyloxy, alkenoyloxy, alkynoyloxy, aryloyloxy or R15 and R16 together form an oxo; R17 and R18 are independently hydrogen, hydroxy, lower alkanoyloxy, alkenoyloxy, alkynoyloxy, aryloyloxy or R17 and R18 together form an oxo; R19 and R20 are independently hydrogen or hydroxy or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; R21 and R22 are independently hydrogen or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy or R21 and R22 together form an oxo; R24 is hydrogen or hydroxy or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; or R23 and R24 together form an oxo or methylene or R23 and R24 together with the carbon atom to which they are attached form an oxirane ring or R23 and R22 together with the carbon atom to which they are attached form an oxetane ring; R25 is hydrogen, hydroxy, or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; or R26 is hydrogen, hydroxy, or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; or R26 and R25 taken together form an oxo; and R27 is hydrogen, hydroxy or lower alkoxy, alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; (e) taxane derivatives disclosed in U.S. Pat. No. 5,227,400 3xe2x80x2-desphenyl-3xe2x80x2-(2-furyl) or 3xe2x80x2-(2-thienyl) derivatives of paclitaxel, Taxotere(copyright); (f) taxane derivatives disclosed in EP 534,709 published Mar. 31, 1993 (paclitaxel derivatives in which the sidechain phenyl groups are independently replaced with naphthyl, styryl or substituted phenyl). See also PCT 92/09589 published Jun. 11, 1992; (g) taxane derivatives disclosed in EP 534,707 published Mar. 31, 1993 (paclitaxel derivatives in which the 3xe2x80x2-N-benzoyl group is replaced with ethoxycarbonyl or methoxycarbonyl); (h) PCT Application 93/06093 published Apr. 1, 1993 (10-desacetoxy derivatives of paclitaxel and Taxotere(copyright)); (i) EP 524,093 published Jan. 20, 1993 (10-, 7-, or 7,10-bis-O-(N-substituted carbamoyl taxane derivatives); (j) 9-xcex1-hydroxy analog of paclitaxel is disclosed in Klein, xe2x80x9cSynthesis of 9-Dihydrotaxol: A New Bioactive Taxane,xe2x80x9d Tetrahedron Letters, 1993, 34(13):2047-2050; (k) 14-xcex2-hydroxy analog of paclitaxel and Taxotere(copyright) prepared from 14xcex2-hydroxy-10-deacetylbaccatin III are disclosed at the 205th ACS National Meeting in Colorado, 1993. (Med. Chem. Division, Abstract No. 28); and (1) other taxanes, such as C7-fluorotaxanes and various C10-substituted taxanes, as disclosed in European Patent Application 577,082A1 published Jan. 5, 1994, which is herein incorporated by reference in its entirety.
The free hydroxy group or groups of taxane derivatives may be converted by conventional methods to the corresponding ester or carbonate; for example in compounds of formula (Ia) one of R1a, R2a or R3a is xe2x80x94OC(O)Rx or xe2x80x94OC(O)ORx and Rx is as previously defined. Thus, a taxane derivative T-OH may be reacted with a compound of the formula L-C(O)ORx (L being a leaving group) such as a chloroformate in the presence of a base such as tertiary amine to give the corresponding carbonate; for example, paclitaxel reacts with ethyl chloroformate in the presence of diisopropylethylamine to provide 2xe2x80x2-O-ethyloxycarbonylpaclitaxel. T-OH may also react with a carboxylic acid RxCO2H or an acylating equivalent thereof (e.g. an anhydride, active ester or an acyl halide) to provide the corresponding ester. Needless to point out when Rx in L-C(O)ORx, or RxCO2H or an acylating equivalent thereof contains hydroxy groups, they are preferably protected with suitable hydroxy protecting groups.
Additionally, taxane derivatives T-[OH]n may be prepared by acylating a taxane moiety having a C13-hydroxy group with an appropriately substituted 3-amino-2-hydroxypropanoic acid, an acylating equivalent thereof, or a precursor thereof. Suitable precursors of substitutd 3-amino-2-hydroxypropanoic acid are for example azetidinones of formula (III). This acylation reaction is exemplified in the coupling of hydroxy protected baccatin III or hydroxy protected 10-deacetylbaccatin III and a phenylisoserine derivative to give paclitaxel derivatives as disclosed in e.g. Denis et al, U.S. Pat. Nos. 4,924,011 and 4,924,012; and in the coupling of a protected baccatin III and an azetidinone to give paclitaxel and derivatives thereof as disclosed in EP Published Application 400,971 published Dec. 5, 1990 (now U.S. Pat. No. 5,175,315) and U.S. Pat. No. 5,229,526.
The process as disclosed in EP 400,971 (the Holton process) involves reacting 1-benzoyl-3-(1-ethoxy)ethoxy-4-phenyl-2-azetidinone with 7-O-triethylsilylbaccatin III in the presence of N,N-dimethylaminopyridine and pyridine at 25xc2x0 C. for 12 hours; paclitaxel is obtained after the various hydroxy protecting groups are removed. An improvement of the Holton process is reported by Ojima et al in xe2x80x9cNew and Efficient Approaches to the Semisynthesis of Taxol and its C-13 Side Chain Analogs by Means of xcex2-Lactam Synthon Methodxe2x80x9d Tetrahedron, 1992, 48(34):6985-7012. Ojima""s process involves first generating the sodium salt of 7-triethylsilylbaccatin III with sodium hydride; this salt is then reacted with chiral 1-benzoyl-3-(1-ethyoxy)ethoxy-4-phenyl-2-azetidinone to provide paclitaxel after removal of the hydroxy protecting groups. In U.S. Pat. No. 5,229,526 Holton discloses the coupling of a metal alkoxide of baccatin III or a derivative thereof with a 2-azetidinone to provide taxanes with C13 sidechain. This process is said to be highly diastereoselective; therefore racemic mixtures of the sidechain precursor 2-azetidinone may be used. Recently, Ojima et al reported in xe2x80x9cA Highly Efficient Route to Taxotere by the xcex2-Lactam Synthon Method,xe2x80x9d Tetrahedron Letters, 1993, 34(26):4149-4152, the coupling of metal alkoxides of 7,10-bis-O-(trichloroethoxycarbonyl)-10-deacetylbaccatin III with chiral 1-(t-butoxycarbonyl)-4-phenyl-3-(protected hydroxy)-2-azetidinone to give Taxotere(copyright) after deprotection. The relevant portions of all references cited above are hereby incorporated by reference.
The baccatin/azetidinone process generalized to the preparation of compounds of formula (Ia) is illustrated in Scheme VI. Again, other taxane derivatives not specifically encompassed within the formula (Ia) may also be prepared by this process by employing appropriate starting materials. 
In Scheme VI, R2xe2x80x2 is hydrogen, and R2d is hydrogen, protected hydroxy or xe2x80x94OC(O)ORx; or R2xe2x80x2 is fluoro, and R2d is hydrogen; R3d is hydrogen, xe2x80x94OC(O)Rx, C1-6alkyloxy, protected hydroxy or xe2x80x94OC(O)ORx; one of R6d or R7d is hydrogen and the other is hydroxy, protected hydroxy or C1-6 alkanoyloxy; or R6d and R7d together form an oxo group; P is a hydroxy protecting group; M is hydrogen or a Group IA metal such as lithium, sodium or potassium; and p, R4, R5 and Rx are as previously defined. The reaction may be conducted according to the procedure disclosed in EP 400,971 wherein the baccatin III derivative of formula (II) wherein M is hydrogen is reacted with an azetidinone of formula (III) in the presence of an organic base such as N,N-dimethylaminopyridine. Preferably, however, the baccatin III derivative is first converted to a 13-alkoxide by treating the former with a strong base such as hydrides, alkylamides, and bis(trialkylsilyl)amides of Group IA metals as disclosed in U.S. Pat. No. 5,229,526 and the Ojima references, supra. More preferably, the 13-alkoxide is a lithium alkoxide. The formation of a lithium salt may be achieved by reacting a compound of formula (II) wherein M is hydrogen with a strong metal base, such as lithium diisopropylamide, C1-6 alkyllithium, lithium bis(trimethylsilyl)amide, phenyllithium, lithium hydride, or the like base. Needless to point out that if a compound of formula (II) contains hydroxy groups in radical Rx, said hydroxy groups are preferably protected with suitable hydroxy protecting groups.
The coupling reaction between a taxane of formula (II) and an azetidinone of formula (III) is conducted in an inert organic solvent such as tetrahydrofuran at reduced temperature in the range of about 0xc2x0 C. to about xe2x88x9278xc2x0 C. The azetidinones of formula (III) may be used as a racemic mixture to couple with taxane metal alkoxides of formula (II) in which M is a group 1A metal; in such case, the azetidinone reactant is preferably used in at least 2 equivalents relative to the taxane reactant, and more preferably from about 3 to about 6 equivalents. Chiral azetidinones may also be used, and in such case one equivalent of the azetidinone relative to the taxane may be sufficient, but preferably the azetidinone is used in slight excess, for example up to 1.5 equivalents.
The hydroxy protecting groups may be the same or they may be chosen in a manner to allow the selective removal of one or more protecting groups without substantially affecting the others; for example, in a compound of formula (Id), R2d and PO may be both triethylsilyloxy, and R3d may be benzyloxycarbonyl; catalytic hydrogenolysis in the presence of palladium on carbon removes the benzyloxycarbonyl protecting group without removing the triethylsilyl group. Thus, the hydroxy protecting groups of a compound of formula (Id) may be selectively removed to provide a compound of formula (Ia).
Compounds of formula (II) are either known in the literature, e.g baccatin III, 10-deacetylbaccatin III and their hydroxy protected derivatives, or can be prepared from the known compounds by conventional conventional methods, e.g converting a hydroxy group to a carbonate. Additional compounds of formula (II) may be prepared according to procedures described hereinbelow in the section PREPARATION OF STARTING MATERIALS.
Compounds of formula (III) can be prepared from a compound of (IIIa) according to the general method described in EP 400,971 and Ojima et al, Tetrahedron, 48:6985-7012, 1992. 
Thus a compound of formula (IIIa) is first treated with a base such as n-butyllithium or triethylamine, and then followed by a compound of the formula R4(O)pCO-L where L is a leaving group to provide a compound of formula (III).
Compounds of (IIIa) may be prepared according to the general method disclosed in EP 400,971 by going through an intermediate compound 3-acetoxy-4-substituted-2-azetidinone (IIIb); or by the method disclosed in U.S. Pat. No. 5,229,526 by going through an intermediate compound 3-triethylsilyloxy-4-substituted-2-azetidinone. In an improved process a compound (IIIb) may be obtained by condensing acetoxyacetyl chloride with a bis-imine followed by hydrogenolysis or acid cleavage to remove the N-imine group; this process is shown in the following scheme in which R5xe2x80x2 is an optionally substituted aryl or a heteroaryl group such as furyl or thienyl. This process is disclosed in co-pending application U.S. Ser. No. 08/165,610 filed Dec. 13, 1993 which is hereby incorporated by reference. 
The products (IIIb) obtained from these cycloaddition reactions are usually a racemic mixture of the two cis-azetidinones. The racemic mixture may be resolved by conventional methods such as conversion to diastereomers, differential absorption on column packed with chiral adsorbents, or enzymatically. For example, a racemic mixture of compounds of formula (IIIb) may be contacted with an enzyme that catalyzes the hydrolysis of an ester, for example an esterase or a lipase, to selectively cleave the 3-acyl group of one enantiomer without affecting the other. (See e.g. Brieva et al, J. Org. Chem., 1993, 58:1068-1075; also co-pending U.S. application Ser. No. 092,170 filed Jul. 14, 1993, European Patent Application Number 552041, published Jul. 21, 1993). Alternatively, the racemic mixture may be first subjected to base-catalyzed hydrolysis to remove the 3-acyl group and to generate a racemic mixture of the corresponding 3-hydroxy xcex2-lactam; the racemic mixture of 3-hydroxy xcex2-lactam is then contacted with an enzyme capable of catalyzing acylation of an hydroxy group to selectively acylate the hydroxy group of one enantiomer without affecting the other. Or the racemic mixture of 3-hydroxy xcex2-lactam may be acylated with a chiral carboxylic acid, and the resulting diastereomeric mixture may then be separated using methods known in the art, and the chiral auxiliary removed to provide the desired enantiomer.
Ojima et al, in J. Org. Chem., 56:1681-1683, 1991; Tet. Lett., 33:5737-5740, 1992; and Tetrahedron, 48:6985-7012, 1992 reported the synthesis of a number of chiral azetidinones of formula (IIIa) and/or the corresponing N-(p-methoxyphenyl) congener; wherein P is the hydroxy protecting group triisopropylsilyl; and R5 is 4-methoxyphenyl, 3,4-dimethyoxyphenyl, phenyl, 4-fluorophenyl, 4-trifluoromethylphenyl, 2-furyl, 2-phenylethenyl, 2-(2-furyl)ethenyl, 2-methylpropyl, cyclohexylmethyl, isopropyl, phenethyl, 2-cyclohexylethyl, or n-propyl. Other references for making azetidinones of formula (IIIa) and/or (III) can be found in European Patent Applications 0,534,709 A1, 0,534,708 A1, and 0,534,707 A1, all three published on Mar. 31, 1993; in PCT application WO 93/06079 published on Apr. 1, 1993; in Bioorganic and Medicinal Chemistry Letters, 3, No. 11, pp 2475-2478 (1993); also in Bioorganic and Medicinal Chemistry Letters, 3, No. 11, pp 2479-2482 (1993); in J. Org. Chem., 58, pp 1068-1075; in Tetrahedron Letters, 31, No. 44, pp 6429-6432 (1990); in Bioorganic and Medicinal Chemistry Letters, 3, No. 11, pp 2467-2470 (1993); European Application 552,041 published on Jul. 21, 1993; and in our copending U.S. application Ser. No. 092,170 filed on Jul. 14, 1993. The relevant portions of all aforementioned references are hereby incorporated by reference. Other azetidinones within the definition of formula (III) but are not specifically disclosed in these references may be prepared by a person skilled in the art following the methodologies generally known in the art.
BIOLOGICAL EVALUATION
Compounds of formula (B) of the present invention are useful intermediates for novel antitumor agents of formula (A). In addition, some compounds within the scope of formula (B), namely compounds of formula (Bxe2x80x2), were themselves found to be antitumor agents. Biological Section I below demonstrates the antitumor activity of the compounds of formula (A). On the other hand, Biological Section II below demonstrates the antitumor activity of the compounds of formula (Bxe2x80x2).
Biological Section I
In vitro cytotoxicity data
The compounds of formula (A) showed in vitro cytoxicity activity against human colon carcinoma cells HCT-116 and HCT-116/VM46. The HCT-116/VM46 cells are cells that have been previously selected for teniposide resistance and express the multi-drug resistance phenotype, including resistance to paclitaxel. Cytotoxicity was assessed in HCT-116 human colon carcinoma cells by XTT (2,3-bis(2-methoxy-4-nitro-5-sulfphenyl)-5-[(phenylamino)carbonyl]2H-tetrazolium hydroxide) assay as reported in D. A. Scudiero, et al., xe2x80x9cEvaluation of soluble tetrazolium/formazan assay for cell growth and drug sensitivity in culture using human and other tumor cell lines,xe2x80x9d Cancer Res. 48:4827-4833, 1988. Cells were plated at 4000 cells/well in 96 well microtiter plates and 24 hours later drugs were added and serial diluted. The cells were incubated at 37xc2x0 C. for 72 hours at which time the tetrazolium dye, XTT, was added. A dehydrogenase enzyme in live cells reduces the XTT to a form that absorbs light at 450 nm which can be quantitated spectrophotometrically. The greater the absorbance, the greater the number of live cells. The results are expressed as an IC50, which is the drug concentration required to inhibit cell proliferation (i.e., absorbance at 450 nm) to 50% of that of untreated control cells. The IC50 values for representative compounds evaluated in this assay are given in Table I.
The compound 7-O-methylthiomethylpaclitaxel (Example 1 (a) was also tested in the cytotoxicity assay and it showed IC50 of 0.003 xcexcM against HCT-116 and 0.025 xcexcM against HCT-116/VM46.)
In vivo antitumor activity
Balb/c x DBA2 F1 (CDF1) hybrid mice were implanted subcutaneously (sc) with 0.1 ml of a 2% (w/v) brei of M109 lung carcinoma (as described in W. Rose xe2x80x9cEvaluation of Madison 109 Lung Carcinoma as a Model for Screening Antitumor Drugs,xe2x80x9d Cancer Treatment Reports, 65, No. 3-4 pp. 299-312 (1981). The test compounds and reference drug, paclitaxel, were administered intravenously to groups of mice; each group received a compound at a different dose level, and three or four different dose levels were evaluated per compound. Mice were followed daily for survival until their death or about day 75 post-tumor implant, whichever occurred first. One group of mice per experiment remained untreated and served as the control. Tumors were also measured once or twice weekly and the size in mm was used to estimate tumor weight according to the published procedure (ibid).
Median survival times of compound-treated (T) mice were compared to the median survival time of parallel control (C) mice. The ratio of the two values for each compound-treated group of mice was multiplied by 100 and expressed as a percentage (i.e., % T/C) in Table II for representative compounds. Additionally, the difference between the median time for treated groups and that for the control group to grow tumor to 1 gm, expressed as T-C values in days, is also shown in Table II. The greater the T-C value, the greater the delay in primary tumor growth. Compounds showing % T/Cxe2x89xa7125% and/or T-Cxe2x89xa74.0 days are considered to be active in the M109 SC model.
Compound of Example 3 (as the triethanolamine salt) was further evaluated in murine and human xenograft tumor models (M109, A2780/cDDPxe2x80x94human ovarian carcinoma resistant to cisplatin, and HCT-116xe2x80x94human colon carcinoma) against paclitaxel as positive control. The A2780/cDDP model is described in Rose and Basler, In Vivo, 1990, 4:391-396; the HCT-116 model is described in Rose and Basler, In Vivo, 1989, 3:249-254. M109 was passaged sc biweekly in Balb/C mice and implanted sc into CDF1 mice for antitumor evaluation. A2780/cDDP and HCT-116 were grown in athymic mice for both passage (every two to three weeks) and therapy experiments. Compound of Example 3 was administered iv in water, or orally in water with a few drops of Tween 80, while paclitaxel was either suspended in water plus Tween 80, or dissolved in cremophore/ethanol (50%/50%) and diluted with saline. The treatment regimen for the sc M109 tumor tests was once daily for 5 consecutive days beginning on Day 4 post tumor implant. For the human tumor xenograft tests, compounds were given once daily every other day for five administrations beginning when the tumors were staged to between 50 to 100 mg.
In one M109 experiment, compound of Example 3 administered iv achieved max. % T/C of 155 (T-C of 19 days) at 36 mg/kg/inj. (cf. paclitaxel max. % T/C of 132 (T-C of 13 days) at 36 or 18 mg/kg/inj.). In the same experiment, compound of Example 3 administered orally achieved a max. % T/C of 158 (T-C of 22.8 days) at a dose of 160 mg/kg/adm. while paclitaxel at the same dose (highest tested) suspended in water and Tween 80 did not show activity. In another M109 experiment, iv administered compound of Example 3 produced max. % T/C of 170 (T-C of 17 days) at 48 mg/kg/inj. (cf. paclitaxel max. % T/C of 167 (T-C of 14 days) at 48 or 36 mg/kg/inj.). In the same experiment, orally administered compound of Example 3 produced max. % T/C of 172 (T-C of 17 days) at a dose of 200 mg/kg/adm. while paclitaxel dissolved in cremophore/ethanol/saline did not show activity at 60/mg/kg/inj. In this experiment, paclitaxel dissolved in cremophore/ethanol/saline could not be administered at greater than 60/mg/kg/inj. due to solubility and toxicity constraints.
In the A2780/cDDP experiment, iv administered compounds of Example 3 showed max. T-C value of 29.8 days at 36 mg/kg/inj (cf. paclitaxel max. T-C of 26.3 days at 36 mg/kg/inj.). Orally administered compound of Example 3 produced max. T-C of 20 days at a dose of 160 mg/kg/adm. In the HCT-116 experiment, iv treatment with 24 or 36 mg/kg/inj. of paclitaxel produced 6 cures of 7 or 6 cures of 8 treated mice, respectively, and 160 or 240 mg/kg/adm. of oral compound of Example 3 cured 6 or 7 of 8 treated mice, respectively. Cure means tumor-free on Day 80 post tumor implant.
The triethanolamine salt of compound of example 1 was also found to have oral activity in the M109 and HCT-116 models.
It is well appreciated in the art that there will be some, usually slight, variations in the anti-tumor activity depending on what particular salt form is employed.
The pharmaceutically acceptable salt of phosphonooxymethyl ethers of taxane derivatives of formula (A) exhibit improved water solubility over paclitaxel thereby allowing more convenient pharmaceutical formulations. Without being bound by theory, it is believed that the phosphonooxymethyl ethers of the present invention are prodrugs of paclitaxel or derivative thereof; the phosphonooxymethyl moiety being cleaved upon contact with phosphatase in vivo to generate subsequently the parent compound.
Biological Section II
Mice M109 Model
Balb/c x DBA/2 F1 hybrid mice were implanted intraperitoneally, as described by William Rose in Evaluation of Madison 109 Lung Carcinoma as a Model for Screening Antitumor Drugs, Cancer Treatment Reports, 65, No. 3-4 (1981), with 0.5 mL of a 2% (w/v) brei of M109 lung carcinoma.
Mice were treated with compound under study by receiving intraperitoneal injections of various doses on either days 1, 5 and 9 post-tumor implant or days 5 and 8 post-implant. Mice were followed daily for survival until approximately 75 -90 days post-tumor implant. One group of mice per experiment remained untreated and served as the control group. Median survival times of compound-treated (T) mice were compared to the median survial time of the control (C) mice. The ratio of the two values for each compound-treated group of mice was multiplied by 100 and expressed as a percentage (i.e. % T/C) in Table III for representative compounds of formula (Bxe2x80x2).
As shown above, compounds of formula (A) and (Bxe2x80x2) of the instant invention are effective tumor inhibiting agents, and thus are useful in human and/or veterinary medicine. Thus, another aspect of the instant invention concerns a method for inhibiting human and/or other mammalian tumors which comprises administering to a tumor bearing host an antitumor effective amount of a compound of formula (A) or (Bxe2x80x2).
Compounds of formulas (A) and (Bxe2x80x2) of the present invention may be used in a manner similar to that of paclitaxel; therefore, an oncologist skilled in the art of cancer treatment will be able to ascertain, without undue experimentation, an appropriate treatment protocol for administering a compound of the present invention. The dosage, mode and schedule of administration for compounds of this invention are not particularly restricted, and will vary with the particular compound employed. Thus a compound of the present invention may be administered via any suitable route of administration, preferably parenterally; the dosage may be, for example, in the range of about 1 to about 100 mg/kg of body weight, or about 20 to about 500 mg/m2. Compounds of formula (A) and (B) may also be administered orally; oral dosage may be in the range of about 5 to about 500 mg/kg of body weight. The actual dose used will vary according to the particular composition formulated, the route of administration, and the particular site, host and type of tumor being treated. Many factors that modify the action of the drug will be taken into account in determining the dosage including age, weight, sex, diet and the physical condition of the patient.
The present invention also provides pharmaceutical compositions (formulations) containing an antitumor effective amount of a compound of formula (A) or (Bxe2x80x2) in combination with one or more pharmaceutically acceptable carriers, excipients, diluents or adjuvants. Examples of formulating paclitaxel or derivatives thereof may be found in, for example, U.S. Pat. Nos. 4,960,790 and 4,814,470, and such examples may be followed to formulate the compounds of this invention. For example, compounds of the present invention may be formulated in the form of tablets, pills, powder mixtures, capsules, injectables, solutions, suppositories, emulsions, dispersions, food premix, and in other suitable forms. They may also be manufactured in the form of sterile solid compositions, for example, freeze dried and, if desired, combined with other pharmaceutically acceptable excipients. Such solid compositions can be reconstituted with sterile water, physiological saline, or a mixture of water and an organic solvent, such as propylene glycol, ethanol, and the like, or some other sterile injectable medium immediately before use for parenteral administration.
Typical of pharmaceutically acceptable carriers are, for example, manitol, urea, dextrans, lactose, potato and maize starches, magnesium stearate, talc, vegetable oils, polyalkylene glycols, ethyl cellulose, poly(vinylpyrrolidone), calcium carbonate, ethyl oleate, isopropyl myristate, benzyl benzoate, sodium carbonate, gelatin, potassium carbonate, silicic acid. The pharmaceutical preparation may also contain nontoxic auxiliary substances such as emulsifying, preserving, wetting agents, and the like as for example, sorbitan monolaurate, triethanolamine oleate, polyoxyethylene monostearate, glyceryl tripalmitate, dioctyl sodium sulfosuccinate, and the like.
In the following experimental procedures, all temperatures are understood to be in Centigrade (C) when not specified. The nuclear magnetic resonance (NMR) spectral characteristics refer to chemical shifts (xcex4) expressed in parts per million (ppm) versus tetramethylsilane (TMS) as reference standard. The relative area reported for the various shifts in the proton NMR spectral data corresponds to the number of hydrogen atoms of a particular functional type in the molecule. The nature of the shifts as to multiplicity is reported as broad singlet (bs), broad doublet (bd), broad triplet (bt), broad quartet (bq), singlet (s), multiplet (m), doublet (d), quartet (q), triplet (t), doublet of doublet (dd), doublet of triplet (dt), and doublet of quartet (dq). The solvents employed for taking NMR spectra are acetone-d6 (deuterated acetone). DMSO-d6 (perdeuterodimethylsulfoxide), D2O (deuterated water), CDCl3 (deuterochloroform) and other conventional deuterated solvents. The infrared (IR) spectral description include only absorption wave numbers (cmxe2x88x921) having functional group identification value.
Celite is a registered trademark of the Johns-Manville Products Corporation for diatomaceous earth.
The abbreviations used herein are conventional abbreviations widely employed in the art. Some of which are: MS (mass spectrometry); HRMS (high resolution mass spectrometry); Ac (acetyl); Ph (phenyl); v/v (volume/volume); FAB (fast atom bombardment); NOBA (m-nitrobenzyl alcohol); min (minute(s)); h or hr(s) (hour(s)); NIS (N-iodosuccinimide); BOC (t-butoxycarbonyl); CBZ or Cbz (benzyloxycarbonyl); Bn (benzyl); Bz (benzoyl); TES (triethylsilyl); DMSO (dimethylsulfoxide); THF (tetrahydrofuran); HMDS (hexamethyldisilazane).
PREPARATION OF STARTING MATERIALS
The preparations of several specific starting materials useful in the preparation of compounds of formula (A) are exemplified below.
Preparation 1. 10-Desacetoxypaclitaxel 
(a) 2xe2x80x2,7-O-bis(2,2,2-trichloroethoxycarbonyl)-10-deacetyl paclitaxel
10-Deacetyl paclitaxel (140 mg, 0.173 mmol) in dry dichloromethane (3.5 mL) was treated at 0xc2x0 C. with pyridine (0.028 mL, 0.346 mmol) and trichloroethyl chloroformate (0.0724 mL, 0.260 mmol). After 1 h at this temperature, the cold bath was removed and the mixture was stirred at room temperature overnight. The solvent was evaporated and the residue chromatographed on silica gel (30-50% ethyl acetate in hexane) to afford the title compound as a foam (92.3 mg, 46%). Further elution afforded unreacted starting material (35 mg, 25%), and 2xe2x80x2,10-O-bis(2,2,2-trichloroethoxycarbonyl)-10-deacetylpaclitaxel in 16% yield.
(b) 2xe2x80x2,7-O-bis(2,2,2-trichloroethoxycarbonyl)-10-desacetoxy-11,12-dihydropaclitaxel-10,12(18)-diene
The product obtained in step (a) (92.3 mg, 0.079 mmol) in dry dichloromethane (2 mL) was treated at room temperature with 1,1,2-trifluoro-2-chlorotriethylamine (0.0384 mL, 0.238 mmol). The solution was stirred overnight. The solvent was evaporated and the residue purified by column chromatography (25% ethyl acetate in hexane) to afford the title compound as a white powder (42.8 mg, 47.3%).
(c) 10-Desacetoxy-11,12-dihydropaclitaxel-10,12(18)-diene
The product of step (b) (39 mg, 0.034 mmol) was dissolved in methanol (0.5 mL) and acetic acid (0.5 mL), and treated with acid-washed zinc dust (66.4 mg, 1.020 mmol). The slurry was heated at 40xc2x0 C. for 1 h, filtered and the filtrate evaporated. Chromatography of the residue with 60% ethyl acetate/hexane gave the title compound as a foam (22 mg, 81%).
(c) 10-Desacetoxypaclitaxel
The product of step (c) (22 mg, 0.028 mmol) in ethyl acetate (0.7 mL) was hydrogenated at atmospheric pressure in the presence of palladium on charcoal (10%, 14.7 mg, 0.014 mmol Pd) After 5.5 h at RT, filtration (rinsing with ethyl acetate), evaporation and chromatography (60% ethyl acetate in hexane) gave the title product (15.0 mg, 68%) as a white foam.
Preparation 2. 7-Deoxy-7xcex1-fluoropaclitaxel 
(a) 2xe2x80x2-O-Benzyloxycarbonyl-7-deoxy-7xcex1-fluoropaclitaxel
Diethylaminosulfur trifluoride (DAST, 18.7 xcexcL, 0.141 mmol) was dissolved in dry dichloromethane (0.5 mL), and this solution was cooled to 0xc2x0 C. A solution of 2xe2x80x2-O-(benzyloxycarbonyl)paclitaxel (71 mg, 0.072 mmol) in dichloromethane (1 mL) was added and the resulting solution was kept at 0xc2x0 C. for 30 min and at room temperature for 4 h. Then, water (0.15 mL) was added to the reaction mixture in order to quench the reaction and the resultant mixture was concentrated to leave a residue. The residue was chromatographed on a silica gel column (being eluted with 40% ethyl acetate in hexane) to yield 61 mg (Y: 85.7%) of a 1:1 mixture of the title compound and 2xe2x80x2-O-benzyloxycarbonyl-8-desmethyl-7,8-cyclopropapaclitaxel.
(b) 7-Deoxy-7xcex1-fluoropaclitaxel
The product mixture obtained in Step (a) (89 mg) was dissolved in ethyl acetate (3 mL) and the mixture was stirred under slightly over one atmospheric pressure of hydrogen in the presence of palladium on charcoal (10% Pd, 29 mg, 0.027 mmol). After 12 h, the solvent was removed, and the residue was purified by silica gel chromatography (being eluted with 40% ethyl acetate in hexane) to afford 67.7 mg of the title compound, along with 8-desmethyl-7,8-cyclopropapaclitaxel.
The following HPLC method was used to separate the 7-deoxy-7xcex1-fluoropaclitaxel and 8-desmethyl-7,8-cyclopropapaclitaxel.
Preparation 3. 7-Deoxy-7xcex1-fluorobaccatin III 
To a dry flask under an inert atmosphere was added 2xe2x80x2-O-(benzyloxycarbonyl)paclitaxel (4 g, 4 mmol) and dry toluene (80 mL). The resulting slurry was stirred at ambient temperature while dry tetrahydrofuran (16 mL) was added dropwise until a colorless solution resulted. The above solution was cooled to xe2x88x9278xc2x0 C. in a dry ice/acetone bath then treated with diethylaminosulfur trifluoride (DAST, 1.2 mL, 2.5 eq.). The reaction mixture was allowed to stir for 16 h as it gradually warmed to ambient temperature. The resulting suspension was filtered and the filtrate (diluted with ethyl acetate (30 mL)) was washed with saturated aqueous sodium bicarbonate followed by brine. The organic fraction was dried (MgSO4) and concentrated to give a crude product as a white foam. The crude material was partially purified by silica gel column chromatography (eluted with 10% CH3CN in CH2Cl2) to afford 1.45 g of a mixture of 2-O-(benzyloxycarbonyl)-7-deoxy-7xcex1-fluoropaclitaxel and 2xe2x80x2-O-(benzyloxycarbonyl)-8-desmethyl-7,8-cyclopropapaclitaxel (82:18 mixture by 1H-NMR).
The above mixture (1.45 g) was taken up in ethyl acetate (60 mL) and treated with palladium on carbon (300 mg). After shaking for 4 h under 50 pounds per square inch (psi) of hydrogen, the reaction was vented and filtered through a short plug of silica gel and concentrated. This furnished the desired product mixture, 7-deoxy-7xcex1-fluoropaclitaxel and 8-desmethyl-7,8-cyclopropapaclitaxel, as a white foam (1.24 g, Y: 99%, 90:10 mixture by 1H-NMR). This mixture was taken up in dry methylene chloride (30 mL) and treated with tetrabutylammonium borohydride (745 mg, 2.9 mmol, 2 eq) and allowed to stir for 6 h. The reaction was then quenched with acetic acid (1 mL), diluted with additional methylene chloride (30 mL) and washed with saturated aqueous sodium bicarbonate solution. The organic fraction was dried (MgSO4) and concentrated. The crude, substituted taxane core mixture was partially purified by silica gel column chromatography (eluted with 10% CH3CN in CH2Cl2) to give a 90:10 mixture (as determined by 1H-NMR) of 7-deoxy-7-xcex1-fluorobaccatin III and 8-desmethyl-7,8-cyclopropabaccatin III (510 mg, 60%) as a white foam. The resulting foam was crystallized from hot isopropanol to give 7-deoxy-7xcex1-fluorobaccatin III (as small white needles (Y: 410 mg); m.p. 234-236xc2x0 C. (decomposition).
Preparation 4. 10-Desacetoxy-7-deoxy-7xcex1-fluoropaclitaxel 
(a) 2xe2x80x2-O-Benzyloxycarbonyl-10-desacetoxypaclitaxel
10-Desacetoxypaclitaxel (27 mg, 0.034 mmol) in dichloromethane (1 mL) was treated with benzyl chloroformate (0.0146 mL, 0.102 mmol), followed by diisopropylethylamine (0.0177 mL, 0.102 mmol). The reaction mixture was stirred at 0xc2x0 C. for 45 min, and at rt for 12 h. Evaporation of the solvent and silica gel chromatography (being eluted with 40% ethyl acetate in hexane) gave 25.5 mg (Y: 81%) of the title compound as a foam.
(b) 10-Desacetoxy-7-deoxy-7xcex1-fluoropaclitaxel
The product obtained in Step (a) (25.5 mg, 0.028 mmol) in dichloromethane (0.8 mL) at 0xc2x0 C. was treated with DAST (0.0071 mL, 0.055 mmol). After 45 min at 0xc2x0 C., the reaction was allowed to proceed for 5 h at rt. Evaporation of the solvent and chromatography gave 2xe2x80x2-O-benzyloxycarbonyl-7-deoxy-7xcex1-fluoropaclitaxel as a crude foam. This compound was dissolved in ethyl acetate (1 mL) and was stirred under slightly over one atmosphere of hydrogen in the presence of palladium on charcoal (10%, 8.9 mg) for 12 h at rt. The catalyst was removed by filtration and silica gel chromatography of the product gave 10 mg (Y: 40% over two steps) of the title product as a foam.
Preparation 5. 10-Deacetyl-7-deoxy-7xcex1-fluoropaclitaxel 
A solution of 2xe2x80x2,10-O-bis(2,2,2-trichloroethoxycarbonyl)-10-deacetylpaclitaxel (120 mg, 0.103 mmol) in dichloromethane (2 mL) was cooled at 0xc2x0 C. and treated with DAST (0.0266 mL, 0.207 mmol). The solution was stirred at 0xc2x0 C. for 30 min and at rt for 4 h. The reaction was quenched by adding water (0.05 mL). The reaction mixture was concentrated and the residue was purified by silica gel chromatography (being eluted with 30% ethyl acetate in hexane) to afford 81 mg (Y: 68%) of 2xe2x80x2,10-O-bis(2,2,2-trichloroethoxycarbonyl)-7-deoxy-7xcex1-fluoropaclitaxel as a foam. This compound (63 mg, 0.054 mmol) was dissolved in methanol (0.5 mL) and acetic acid (0.5 mL) and treated with zinc dust (104 mg, 1.62 mmol) for 90 min at 45xc2x0 C. The reaction mixture was filtered and the filtrate was concentrated. Silica gel chromatography (being eluted with 40% hexane in 60% ethyl acetate) of the residue afforded 38 mg (Y: 86%) of the title compound as a white solid.
Preparation 6. 7-Deoxybaccatin III 
(a) 7-O-[(Methylthio)thiocarbonyl]baccatin III
Baccatin III (750 mg, 1.278 mmol) was dissolved in dry tetrahydrofuran (20 mL) and imidazole (8.7 mg, 0.128 mmol) was added in one lot. Sodium hydride (50% in mineral oil, 77 mg, 1.597 mmol) was added at room temperature. When gas evolution had ceased (10 min), carbon disulfide (4.6 mL) was added at once. After 3 h at room temperature, the yellow solution was treated with methyl iodide (0.238 mL, 3.835 mmol) and stirred overnight. Work-up with ethyl acetate and water gave the title compound as a crude oil.
Alternate Run:
Baccatin III (394 mg, 0.672 mmol) was dissolved in tetrahydrofuran (5 mL) and carbon disulfide (1 mL). To this solution was added sodium hydride (40.3 mg, 60%, 1.009 mmol). A catalytic amount of imidazole was also added. The reaction mixture was stirred at room temperature for 1.5 h. and then methyl iodide (122.8 xcexcL, 2.016 mmol) was added. After 40 min, the solvent was removed in vacuo, and the residue was chromatographed on silica gel (eluted with 20%-50%-60% ethyl acetate in hexanes) to afford the title product (260 mg, Y: 57.2%) together with 7-epi baccatin (98.5 mg, 25%).
(b) 7-O-[(Methylthio)thiocarbonyl]-13-O-triethylsilylbaccatin III
The product of step (a) as a crude oil was dissolved in dry dimethylformamide (5 mL) and treated with imidazole (870 mg, 12.78 mmol) and triethylsilyl chloride (2.10 mL, 12.78 mmol) at room temperature for 15 h. Addition of water was followed by extraction into ethyl acetate. The organic layer was washed extensively with water, and then dried. Silica gel flash chromatography (being eluted with 20% ethyl acetate in hexanes) gave the title compound as a glassy solid (Y: 209 mg, 20% yield over two steps).
Alternate Run:
The product of step (a) (193.4 mg, 0.286 mmol) was dissolved in dry dimethylformamide (2.86 mL). To this solution was added imidazole (77.9 mg, 1.14 mmol), followed by triethylsilyl chloride (192 xcexcL, 1.14 mmol). The reaction mixture was stirred overnight at room temperature. After 12 h, the reaction mixture was diluted with ethyl acetate (150 mL). The organic layer was washed with water (3xc3x9710 mL) and brine (1xc3x9710 mL), dried, and concentrated in vacuo. The residue was chromatographed on silica gel (eluted with 20% Ethyl acetate in hexanes) to afford the title product (163 mg,Y: 72.0%).
(c) 7-Deoxy-13-O-triethylsilylbaccatin III
The product of step (b) (182 mg, 0.230 mmol) in dry benzene (5 mL) was heated to 80xc2x0 C. in the presence of tributyltin hydride (0.310 mL, 1.150 mmol) and 2,2xe2x80x2-azobisisobutyronitrile (AIBN, 10 mg). After 3 h the solution was allowed to cool, and the solvent evaporated in vacuo. Silica gel chromatography of the residue (being eluted with 20% ethyl acetate in hexane) gave the title compound as an oil.
(d) 7-Deoxybaccatin III
The product of step (c) was dissolved in tetrahydrofuran (5 mL) and treated with tetrabutylammonium fluoride (1M in tetrahydrofuran, 0.50 mL, 0.50 mmol) for 2 h at room temperature. Dilution with ethyl acetate and washing with water and brine, followed by silica gel chromatography (being eluted with 1:1 ethyl acetate/hexane) gave the title compound as a white glassy solid (63 mg, Y: 58% over two steps).
Preparation 7. 10-Desacetoxybaccatin III 
(a) 10-Deacetyl-10-O-(pentafluorophenoxy)thiocarbonyl-7-O-triethylsilylbaccatin III
7-O-Triethylsilyl-10-deacetylbaccatin III (see Greene et al, J. Am. Chem. Soc., 110, p. 5917, 1988) (319 mg, 0.485 mmol) was dissolved in dry tetrahydrofuran (5 mL), cooled to xe2x88x9240xc2x0 C., and treated with n-butyllithium (1.58M in hexanes, 0.384 mL, 0.606 mmol). After 40 min at this temperature, pentafluorophenyl chlorothionoformate (0.086 mL, 0.536 mmol) was added neat by syringe. The reaction mixture was stirred at xe2x88x9220xc2x0 C. for 90 min, quenched with saturated ammonium chloride solution, and extracted with ethyl acetate. The ethyl acetate layer was dried and concentrated. The residue was purified by silica gel chromatography (being eluted with 40% ethyl acetate in hexane) to afford the title compound as a foam (320 mg, Y: 74%).
(b) 10-Desacetoxy-7-O-triethylsilylbacctain III
The product of step (a) (119 mg, 0.135 mmol) was dissolved in dry toluene (3 mL) and treated with AIBN (2 mg). The solution was degassed with dry nitrogen, then tributyltin hydride (0.055 mL, 0.202 mmol) was added. Subsequently, the solution was heated at 90xc2x0 C. for 1 h. The solvent was then evaporated and silica gel chromatography of the residue (being eluted with 40% ethyl acetate in hexane) gave the title compound (87 mg, Y: 99%) as a colorless foam.
(c) 10-Desacetoxybaccatin III
The product of step (b) (120 mg, 0.187 mmol) was dissolved in acetonitrile (3.5 mL) and the solution was cooled to xe2x88x9210xc2x0 C. Concentrated HCl (36%, 0.060 mL) was added, and the solution was stirred for 30 min. The mixture was diluted with ethyl acetate (75 mL), and washed with saturated aqueous sodium bicarbonate and brine, then dried and concentrated. The residue was purified by flash silica chromatography (being eluted with 70% ethyl acetate in hexane) to afford 10-deacetyloxybaccatin III as a foam (75 mg, Y: 76%).
Preparation 8. 10-Desacetoxy-7-deoxybaccatin III 
(a) 7-O-[(Methylthio)thiocarbonyl]-10-desacetoxybaccatin III
10-Desacetoxybaccatin III (75 mg, 0.142 mmol) was dissolved in dry tetrahydrofuran (2 mL) and carbon disulfide (0.5 mL). Sodium hydride (60% in mineral oil, 8.5 mg, 0.213 mmol) was then added, and the mixture was stirred at room temperature for 2 h. Iodomethane (0.026 mL, 0.426-mmol) was added, and the reaction was allowed to proceed overnight. The solvent was then removed and the residue was purified by silica gel chromatography (being eluted with 50-70% ethyl acetate in hexane) to give the title compound as a foam (46.4 mg, Y: 53%).
(b) 10-desacetoxy-7-deoxy-baccatin III
The product of step (a) (36 mg, 0.058 mmol) was refluxed in benzene (1 mL) in the presence of AIBN (2 mg) and tributyltin hydride (0.079 mL, 0.290 mmol) under an argon atmosphere for 3 h. Concentration of the reaction mixture and flash silica gel chromatography of the residue (being eluted with 40% ethyl acetate in hexanes) followed by HPLC (high pressure liquid chromatography) separation from other components afforded the title compound as a foam (16.8 mg, Y: 56%).
Alternate Run:
To a solution of 7-O-[(methylthio)carbonothioyl]-13-O-triethylsilylbaccatin III (product of preparation I, step (b), 416.3 mg, 0.527 mmol) in dry toluene (10.5 mL) was added catalytic amount of AIBN, and the resulting solution was degassed with dry N2 for 5 min. Tributyltin hydride (708.7 uL, 2.63 mmol) was the added and the reaction mixture was heated at 100xc2x0 C. for 2 h., after which another portion of tributyltin hydride (425.3 uL, 1.581 mmol) was added. The reaction mixture was heated for 5.5 h at 100xc2x0 C., and then allowed to cool to room temperature. Silica gel chromatography (eluted with 20% ethyl acetate in hexanes) afforded 7-deoxy-10-desacetoxy-13-O-(triethysilyl)baccatin III (320 mg, Y: 97%).
To a solution of the product of the above step (160 mg, 0.255 mmol) in dry tetrahydrofuran (2 mL) at room temperature was added tetrabutylammonium fluoride (766 uL, 1M, 0.766 mmol). The reaction mixture was stirred for 1 h at room temperature. The solvent was removed and the residue was chromatographed on silica gel (eluted with 50-70% ethyl acetate in hexanes) to afford the desired title product (115 mg, Y: 87.9%).
Preparation 9. (3R, 4S)-1-t-Butoxycarbonyl-4-phenyl-3-triethylsilyloxy-2-azetidinone 
To a stirred solution of (3R,4S)-4-phenyl-3-triethylsilyloxy-2-azetidinone (2.200 g, 7.92 mmol) in dry tetrahydrofuran (25 mL) was added N,N-diisopropylethylamine (1.65 mL. 9.510 mmol, 1.2 equiv) at 0xc2x0 C. under an argon atmosphere. The solution was stirred for 5 min followed by the addition of di-t-butyl dicarbonate (2.080 g, 9.510 mmol, 1.2 equiv) and 4-dimethylaminopyridine (193.6 mg, 1.581 mmol, 0.20 equiv). The reaction mixture was stirred at 0xc2x0 C. for 60 min., then diluted with ethyl acetate (25 mL). The resulting solution was washed with brine, 10% NaHCO3, 10% HCl solution, dried (MgSO4), and concentrated to give a crude compound (oil). The compound was further purified by silica gel flash chromatography (being eluted with 15% ethyl acetate in hexanes) to afford the title compound as a white solid (2.4 g, Y: 83%).
Preparation 10. (xc2x1)-cis-3-Acetyloxy-4-phenylazetidin-2-one 
(a) To a 1 L, 3-necked round bottom flask equipped with a thermometer, magnetic stirrer and dropping funnel was added hydrobenzamide (30.00 g, 100.5 mmol) and ethyl acetate (150 mL). With stirring and under a blanket of argon, the reaction mixture was cooled to 5xc2x0 C. and triethylamine (16.8 mL, 121 mmol) was added. A solution of acetoxyacetyl chloride (12.4 mL, 116 mmol) in ethyl acetate (300 mL) was then added dropwise over a 90 min period. After 16 h at this temperature, the reaction mixture was allowed to warm to 20xc2x0 C. (1.5 h) and transferred to a separatory funnel. The organic layer was washed successively with aqueous NH4Cl (sat) (150 mL, 100 mL), aqueous NaHCO3 (saturated) (120 mL) and brine (120 mL). For purposes of characterization, the title compound can be isolated at this stage by drying the organic phase over MgSO4, filtering, and removing the solvent in vacuo. This provided (xc2x1)-cis-3-acetyloxy-1-[(phenyl)(benzylidenimino)methyl]-4-phenylazetidin-2-one in quantitative crude yield as a red glass.
(b) A solution of the compound obtained in part (a) in ethyl acetate (500 mL) was carefully transferred, under a stream of argon, to a 2.0 L Parr flask containing 10% palladium on activated charcoal (6.00 g). This mixture was treated with hydrogen (4 atm) for 20 h whereupon the catalyst was removed by filtration through a pad of Celite. The filter cake was slurried in ethyl acetate (200 mL), stirred (10 min) and filtered. The filter cake was rinsed with ethyl acetate (100 mL) and the filtrates combined. The organic layer was washed with 10% HCl (300 mL) and both layers filtered through a sintered glass funnel to remove the white precipitate (dibenzylaminexe2x80xa2HCl) which was rinsed with ethyl acetate (100 mL). The phases were separated and the organic layer was washed with another portion of 10% HCl (200 mL). The combined 10% HCl washes were re-extracted with ethyl acetate (200 mL) and the combined organic layers were washed with aqueous NaHCO3 (saturated) (300 mL) and brine (250 mL). The organic layer was dried over MgSO4, filtered and concentrated in vacuo to a final volume of 75 mL. This mixture was cooled to 4xc2x0 C. and the precipitated product isolated by filtration. The filter cake was washed with hexane (200 mL) to provide 16.12 g (78.1% overall yield from hydrobenzamide) of the title compound as white needles.
mp=150-151xc2x0 C.
Preparation 11. (xc2x1)- cis-3-Triethylsilyloxy-4-(2-furyl)-N-t-butoxycarbonylazetidin-2-one 
(a) The procedure described in Preparation 10, part (a), was followed except that hydrofuramide [i.e. 2-furyl-CH-(Nxe2x95x90CH-2-furyl)2] was used instead of hydrobenzamide and the reaction was performed on 18.6 mmol (vs 100 mmol) scale. Thus, hydrofuramide (5.00 g, 18.6 mmol), triethylamine (3.11 mL, 22.3 mmol) and acetoxyacetyl chloride (2.30 mL, 21.4 mmol) gave 6.192 g (Y: 90.4%) of (xc2x1)-cis-3-acetyloxy-1-[(2-furyl)(2-furylmethylenimino)methyl]-4-(2-furyl)azetidin-2-one as a pale red syrup.
(b) The procedure described in Preparation 10, part (b), was followed except that the product was isolated by preparative TLC and the reaction was performed on the 2.7 mmol scale based on the original amount of hydrofuramide. Thus, the crude product obtained in part (a) above was re-dissolved in ethyl acetate (50 mL) and added to 10% palladium on activated charcoal (150 mg). Purification of the crude solid by preparative TLC (2 mm silica gel, eluted with 1:1 ethyl acetate/hexane) gave 386 mg (65.8% corrected overall yield from hydrofuramide) (xc2x1)-cis-3-(acetyloxy)-4-(2-furyl)azetidin-2-one as a yellow solid. This was recrystallized from ethyl acetate/hexane.
mp=118-119xc2x0 C.
(c) The compound obtained in part (b) above (3.78 g, 19.4 mmol) in 60 mL of methanol was stirred with K2CO3 (20 mg, 0.14 mmol) for 90 min and the solution neutralized with Dowex 50W-X8 and filtered. The filtrate was concentrated and the residue dissolved in 80 mL of anhydrous THF and stirred at 0xc2x0 C. with imidazole (1.44 g, 21.2 mmol) and TESCl (3.4 mL, 20.2 mmol) for 30 min. The solution was diluted with ethyl acetate and washed with brine, dried over MgSO4 and concentrated. The residue was chromatographed over silica gel (eluted with 3:1 hexane/ethyl acetate) to give 4.47 g (Y: 86%) of (xc2x1)- cis-3-triethylsilyloxy-4-(2-furyl)-azetidin-2-one as a colorless oil.
(d) The product of part (c) (2.05 g, 7.7 mmol) in 30 mL of dichloromethane was stirred at 0xc2x0 C. with diisopropylethyl amine (1.5 mL, 8.6 mmol) and di-t-butyl dicarbonate (2.0 g, 9.2 mmol) in addition to a catalytic amount of dimethylaminopyridine (DMAP). The solution was diluted with dichloromethane and washed with brine, dried over MgSO4 and concentrated. The residue was chromatographed over silica gel (eluted with 8:1 hexane/ethyl acetate) to give 2.0 (Y: 70%) of the title compound as a waxy solid.
The racemic mixture obtained in part (b) may be used as substrate for enzymatic hydrolysis using a lipase such as PS-30 from Pseudomonas sp. (Amano International Co.) to give (3R,4R)-3-hydroxy-4-(2-furyl)-azetidin-2-one. The method of enzymatic resolution using the lipase PD-30 and other enzymes is disclosed in our co-pending application U.S. Ser. No. 092,170, filed Jul. 14, 1993 which is hereby incorporated by reference in its entirety.
The procedure in parts (c) and (d) was followed using (3R,4R)-3-hydroxy-4-(2-furyl)-azetidin-2-one to provide (3R,4R)-N-(t-butoxycarbonyl)-3-triethylsilyoxy-4-(2-furyl)azetidine-2-one.
Preparation 12. (xc2x1)- cis-3-Triethylsilyloxy-4-(2-thienyl)-N-t-butoxycarbonylazetidin-2-one 
(a) The procedure described in Preparation 10, step (a) was followed except that hydrothienamide [i.e. 2-thienyl-CH-(Nxe2x95x90CH-2-thienyl)2] was used instead of hydrobenzamide. Thus, hydrothienamide (30 g, 94.7 mmol), thiethylamine (15.84 mL, 114 mmol) and acetoxyacetyl chloride (11.6 mL, 108 mmol) provided (xc2x1)-cis-3-acetyloxy-1-[(2-thienyl)(2-trienylmethylenimino)methyl]-4-(2-thienyl)azetidin-2-one as viscous oil.
(b) A 70% aqueous solution of acetic acid (0.35 mL glacial acetic acid and 0.15 mL water) was added in one portion to a stirred solution of the product obtained in part (a) (0.431 g, 1.03 mmol) in dichloromethane (2.93 ml) at 25xc2x0 C. The reaction mixture was brought to reflux and stirred for 2.5 h. The reaction was diluted with 50 mL dichloromethane and then washed with two 75 mL portions of saturated aqueous sodium bicarbonate and then one 50 mL portion of saturated brine. The organic extract was concentrated in vacuo to a brown oil, dissolved in a minimal amount of dichloromethane, and then placed on a silica gel column measuring 4xe2x80x3 by 0.5xe2x80x3. Elution using a gradient of 10 through 60% EtOAc in hexane provided less polar sideproducts and then (xc2x1)-cis-3-acetyloxy-4-(2-thienyl)azetidin-2-one (0.154 g, Y: 75%) as a white solid.
(c) A solution of the product obtained in part (b) (2.5 g, 11.8 mmol) was dissolved in methanol (10 mL) and treated with saturated aqueous sodium bicarbonate (10 mL) and the resulting slurry was allowed to stir at ambient temperature for 3 h. The reaction was then diluted with ethyl acetate (20 mL) and washed with water (15 mL). The aqueous fraction was back extracted several times with ethyl acetate and the combined organic fractions were dried (MgSO4) and concentrated to give a yellow solid (Y: 1.7 g). The crude material was dissolved in dry tetrahydrofuran (20 mL) and the solution was cooled to 5xc2x0 C. in an ice/water bath. Imidazole (752 mg, 1.1 eq) was then added. After stirring 5 min, triethylchlorosilane (1.85 mL, 1.1 eq) was added dropwise. The resulting suspension was allowed to stir for 3 h at that temperature; then the solids were removed by filtration. The organic fraction was washed with water (2xc3x9720 mL) then dried (MgSO4) and concentrated. The crude product was purified by silica gel column chromatography (eluted with hexanes/ethyl acetate 7:3) to give (xc2x1)-cis-3-triethylsilyloxy-4-(2-thienyl)-azetidin-2-one as a colorless solid (1.5 g, Y: 45%). m.p. 70-71xc2x0 C.
Alternate Run:
The product obtained in part (b) (2.0 g, 9.37 mmol) in 40 mL of methanol was stirred with K2CO3 (60 mg, 0.43 mmol) for 30 min and the solution neutralized with Dowex 50W-X8 and filtered. The filtrate was concentrated and the residue dissolved in 50 mL of anhydrous THF and stirred at 0xc2x0 C. with imidazole (0.85 g, 11.3 mmol) and TESCl (1.9 mL, 12.5 mmol) for 30 min. The solution was diluted with ethyl acetate and washed with brine, dried over MgSO4 and concentrated. The residue was chromatographed over silica gel (eluted with 3:1 hexane/ethyl acetate) to give 2.13 g (Y: 86%) of the title product as a colorless oil.
(d) A solution of the product obtained in part (c) (425.7 mg, 1.48 mmol) was dissolved in dichloromethane (10 mL) and cooled to 5xc2x0 C. in an ice/water bath. The reaction was treated with a catalytic amount of DMAP followed by diisopropylethylamine (TESCl, 0.25 mL, 1.0 eq) then by di-t-butyl dicarbonate (388.4 mg, 1.2 eq). After stirring 2 h at that temperature the reaction was quenched with saturated aqueous sodium bicarbonate (5 mL) and the organic fraction was washed with water (5 mL) then dried (MgSO4), passed through a short plug of silica gel and concentrated to give the desired product as a colorless oil (525.3 mg, Y: 93%).
Prepartion 13. (3R, 4R)-3-Triethylsilyloxy-4-(2-furyl)-N-n-butyloxycarbonylazetidin-2-one 
(3R,4R)-3-Triethylsilyloxy-4-(2-furyl)azetidin-2-one (0.58 g, 2.17 mmol) in 30 mL of dichloromethane was stirred with diisopropylethyl amine (0.4 mL, 2.30 mmol) and butylchloroformate (0.3 mL, 2.36 mmol) in addition to a catalytic amount of DMAP. The solution was stirred for 1 h and diluted with dichloromethane and washed with brine, dried over MgSO4 and concentrated. The residue was chromatographed over silica gel (eluted with 3:1 hexane/ethyl acetate) to give 523 mg of product (Y: 65%); IR(KBr) 1820, 1734, 1318, 1018, 734 cmxe2x88x921; 1H-NMR (CDCl3, 300 MHz) xcex4 7.38 (m, 1H), 6.35 (m, 2H), 5.09 (ABq, J=15.5, 5.6 Hz, 2H), 4.14 (m, 2H), 1.56 (m, 2H), 1.28 (s, 2H), 0.87 (t, J=8.7 Hz, 3H), 0.82 (t, J=7.9, 9H), 0.50 (m, 6H); 13C-NMR (CDCl3, 75.5 Hz) xcex4 165.4, 149.1, 147.6, 142.9, 110.5, 109.9, 77.7, 66.6, 55.9, 30.5, 18.8, 13.6, 6.3, 4.3; DCIMS M+H calcd for C18H29NO5Si: 368, Found: 368.
Preparation 14. (3R,4R)-3-Triethylsilyloxy-4-(2-furyl)-N-isopropyloxycarbonylazetidin-2-one 
(3R, 4R) -3-Triethylsilyloxy-4-(2-furyl)azetidin-2-one (0.51 g, 1.91 mmol) in 25 mL of dichloromethane was stirred with diisopropylethyl amine (0.78 mL, 4.4 mmol) and i-propylchloroformate (4.0 mL, 1.0M in toluene, 4.0 mmol) in addition to a catalytic amount of DMAP. The solution was stirred for 1 h and diluted with dichloromethane and washed with brine, dried over MgSO4 and concentrated. The residue was chromatographed over silica gel (eluted with 5:1 hexane/ethyl acetate) to give 649 mg of the title product (Y: 96%); IR(KBr) 1822, 1812, 1716, 1374, 1314, 1186, 1018, 1004, 746 cmxe2x88x921; 1H-NMR (CDCl3, 300 MHz) xcex4 7.39 (m, 1H), 6.35 (m, 2H), 5.08 (ABq, J=15.6, 5.6 Hz, 2H), 4.96 (d, J=10.0 Hz, 1H), 1.25 (d, J=6.3 Hz, 3H), 1.17 (d, J=6.3 Hz, 3H)), 0.83 (t, J=7.8, 9H), 0.50 (m, 6H); 13C-NMR (CDCl3, 75.5 Hz) xcex4 165.5, 148.6, 147.8, 142.9, 110.5, 109.9, 77.6, 71.1, 55.9, 21.7, 21.6, 6.3, 4.4; DCIMS M+H calcd for C17H28NO5Si: 354, Found: 354.
Preparation 15. (xc2x1)-cis-3-Triethylsilyloxy-4-isobutenyl-N-t-butoxycarbonylazetidin-2-one
(a) N-4-methoxy-N-(3-methyl-2-butenyl)benzenamine 
A solution of p-anisidine (5.7 g, 46.3 mmol) was dissolved in diethylether (100 mL) and was treated with a catalytic amount of p-toluensulfonic acid (10 mg). To this was added 3-methyl-2-butenal (2.67 mL, 50.9 mmol) in one portion and the reaction was allowed to stir at ambient temperature for 16 h. The solvent was then evaporated on a rotary evaporator at 0.5 torr to furnish the desired imine (8.7 g, 100%) as a brown oil; 1H NMR 300 MHz, CDCl3): xcex4 8.38 (d, 1H, J=9.5 Hz), 7.11 (dd, 2H, J=2.2, 6.7 Hz), 6.88 (dd, 2H, J=2.2, 6.7 Hz), 6.22-6.18 (m, 1H), 3.81 (s, 3H), 2.01 (s, 3H), 1.95 (s, 3H).
(b) (xc2x1)-cis-N-(4-methoxyphenyl)-3-acetyloxy-4-isobutenylazetidin-2-one 
A solution of acetoxyacetyl chloride (6.9 g, 50.5 mmol) was dissolved in ethyl acetate (100 mL) and cooled to xe2x88x9230xc2x0 C. under an inert atmosphere. To this solution was added triethylamine (7.0 mL, 50.5 mmol) over a 5 min period. The resulting white slurry was then treated with an ethyl acetate solution of N-4-methoxy-N-(3-methyl-2-butenyl)benzenamine (8.7 g, 40 mL) dropwise over a 20 min period. The resulting green-brown slurry was then gradually allowed to warm to ambient temperature over a 4 h period. The slurry was then filtered through a pad of celite and the filtrate was washed with water then brine. The organic fraction was dried (MgSO4) and concentrated to give a brown oil. The crude product was purified by careful silica gel chromatography (eluted with hexanes/ethyl acetate 8:2) to furnish an orange oil which solidified on standing. This was recrystallized from dichloromethane/hexanes to furnish the desired product as a pale yellow solid (4.4 g, 32%); 1H NMR (300 MHz, CDCl3): xcex4 7.32 (d, 2H, J=9.1 Hz), 6.86 (d, 2H, J=9.1 Hz), 5.59 (dd, 1H, J=3.0, 7.8 Hz), 5.14-5.10 (m, 1H), 4.96 (dd, 1H, J=4.8, 9.3 Hz), 3.77 (s, 3H), 2.11 (s, 3H,), 1.81 (s, 3H), 1.78 (s, 3H).
(c) (xc2x1)-cis-3-Acetyloxy-4-isobutenylazetidin-2-one 
A solution of the (xc2x1)-cis-N-(4-methoxyphenyl)-3-acetyloxy-4-isobutenylazetidin-2-one (4.88 g, 16.2 mmol) was dissolved in acetonitrile (50 mL) and cooled to 0-5xc2x0 C. in an ice bath. To this was added a cold solution of ceric ammonium nitrate (26.6 g, 48.6 mmol, 50 mL) in one portion. The deep red reaction was allowed to stir for 10 min and during that time the color gradually lightened to orange. The cold solution was transferred to a separatory funnel, diluted with water, and extracted with ethyl acetate. The organic fraction was washed with several portions of 10% aqueous sodium sulfite, followed by saturated aqueous sodium bicarbonate. The organic fraction was dried (MgSO4) and concentrated to give the desired product (2.71 g, 91%) as a yellow-orange solid that was used directly in the next step; 1H NMR (300 MHz, CDCl3): xcex4 6.11 (bs, 1H), 5.73 (dd, 1H, J=2.2, 4.7 Hz), 5.12-5.08 (m, 1H), 4.63 (dd, 1H, 4.7, 9.1 Hz), 2.09 (s, 3H), 1.75 (s, 3H), 1.67 (s, 3H).
(d) (xc2x1)-cis-3-Triethylsilyloxy-4-isobutenylazetidin-2-one 
(xc2x1)-cis-3-Acetyloxy-4-isobutenylazetidin-2-one (1.47 g, 8.0 mmol) was dissolved in methanol (15 mL) and was stirred with K2CO3 (110.5 mg, 0.8 mmol) for 3 h at ambient temperature. The solution was then neutralized with Dowex 50W-X8resin and then filtered. The filtrate was concentrated and the crude solid was dissolved in THF (25 mL) and cooled to 5xc2x0 C. in an ice bath. Imidazole (544.0 mg, 8.0 mmol) was added and once dissolved, triethylsilyl chloride (1.34 mL, 8.0 mmol) was added dropwise via syringe. The resulting slurry was allowed to warm to ambient temperature and stir overnight. The solution was filtered and the filtrate was washed with water, then brine. The organic fraction was dried (MgSO4) and concentrated. The crude solid was purified by silica gel chromatography (eluted with hexanes/ethyl acetate 3:1) to furnish the desired product (612 mg, 30%) as a pale yellow solid; 1H NMR (300 MHz, CDCl3): xcex4 5.87. (bs, 1H), 5.31-5.26 (m, 1H), 4.90 (dd, 1H, J=2.2, 4.7 Hz), 4.42 (dd, 1H, J=4.7, 9.3 Hz), 1.74 (s, 3H), 1.28 (s, 3H), 0.98-0.91 (m, 9H), 0.71-0.55 (m, 6H).
(e) (xc2x1)-cis-3-Triethylsilyloxy-4-isobutenyl-N-t-butoxycarbonylazetidin-2-one 
(xc2x1)-cis-3-Triethylsilyloxy-4-isobutenylazetidin-2-one (1.01 g, 3.95 mmol) was dissolved in dichloromethane (20 mL) and was treated with diisopropylethylamine (0.68 mL, 3.95 mmol) and a catalytic amount of dimethylaminopyridine. To this solution was added di-t-butyl dicarbonate (1.02 g, 4.68 mmol) and the solution was allowed to stir for 24 h at ambient temperature. The solution was then diluted with additional dichloromethane and washed with water then brine. The organic fraction was dried (MgSO4) and concentrated. The residue was purified by silica gel chromatography (eluted with hexanes/ethyl acetate 8:2) to give the desired product (1.26 g, 90%) as a colorless oil; 1H NMR (300 MHz, CDCl3): xcex4 5.24 (d, 1H, J=9.6 Hz), 4.86 (d, 1H, J=5.7 Hz), 4.72 (dd, 1H, J=6.0, 9.9 Hz), 1.78 (d, 3H, J=1.1 Hz), 1.75 (d, 3H, J=1.1 Hz), 1.47 (s, 9H), 0.96-0.91 (m, 9H), 0.64-0.55 (m, 6H).
The procedure described above in Preparations 9, 11(d), 12(d), 13, 14, and 15(e) may be adapted to the preparation of other N-substituted azetidinones useful in the preparation of compounds of the invention. Examples of such azetidinones are listed in the following table; P below is a hydroxy protecting group such as triethyl silyl, triisopropylsilyl and ethoxyethyl.
Preparation 16. 10-deoxytaxotere 
10-Desacetoxy-7-O-triethylsilylbaccatin III (100 mg, 0.156 mmol) was placed in a flask under argon and dissolved in dry tetrahydrofuran (1.5 mL). Upon cooling to xe2x88x9240xc2x0 C., n-butyllithium (1.45M in hexanes, 0.119 mL, 0.170 mmol) was added dropwise, followed by (3R,4S)-1-tert-butoxycarbonyl-4-phenyl-3-triethylsilyloxy-2-azetidinone (94.2 mg, 0.25 mmol) in tetrahydrofuran (0.5 mL) over a period of 2 min. The mixture was immediately warmed to 0xc2x0 C. and stirred for 45 min before being quenched with saturated ammonium chloride (3 mL). The mixture was extracted with ethyl acetate, dried, and concentrated. Silica gel chromatography (eluted with 30% ethyl acetate in hexane) afforded 10-deoxy-2xe2x80x2,7-bis-O-(triethylsilyl)taxotere as a foam (125 mg, Y: 76%). This compound (100 mg, 0.098 mmol) was immediately dissolved in acetonitrile (2 mL) at xe2x88x925xc2x0 C. and treated with hydrochloric acid (0.037 mL, 36%, 12M). The mixture was stirred for 2 h at xe2x88x925xc2x0 C., then quenched with aqueous bicarbonate, extracted with ethyl acetate, and dried. Evaporation of the solvent was followed by silica gel chromatography (eluted with 75% ethyl acetate in hexane) to afford the title compound as a foam (80.5 mg, Y: 80%).
The general procedure provided in Preparation 16 may be adapted to the preparation of other compounds of formula (Ia) by starting with the appropriate baccatin III component and the azetidinone component; examples of other compounds of formula (Ia) are listed in the following table. It will be understood that even though the compounds below are shown with free hydroxy groups, with the judicious selection of the various hydroxy protecting groups, any one of the protecting groups at the 2xe2x80x2-, 7- or 10- position may be selectively removed without affecting other protecting groups present.
Preparation 17. Bis(methylthiomethyl)ether
CH3SCH2OCH2SCH3 
Sodium iodide (8.23 g, 55.23 mmol) was added to a solution of 1,1xe2x80x2-dichlorodimethyl ether (3.0 g, 26.3 mmol) in acetone (100 ml) at 0xc2x0 C. and the mixture was stirred at this temperature for 20 min. Sodium thiomethoxide (1.84 g, 5.23 mmol) was then added in four portions and the resulting solution was stirred for an additional 1 h. The heterogeneous solution was then filtered through a pad of celite and the filtrate concentrated in vacuo. The residual oil was partitioned between ethyl acetate and saturated aqueous sodium bicarbonate solution. The aqueous layer was removed and further extracted with ethyl acetate. The combined organics were then treated with a 1:1 (v:v) mixture of saturated aqueous sodium bicarbonate and 5% aqueous sodium thiosulfate solution. The organics were then washed with brine, dried over sodium sulfate and concentrated in vacuo. The residual oil was purified via flash chromatography (30:1, hexanes:ethyl acetate) to provide 1.9 g of a yellow oil which was subsequently distilled using a kugelrhor apparatus (120-130xc2x0 C., 20 mmHg) yielding 1.5 g (45%) of the title compound as colorless oil:
1H NMR (300 MHz, CDCl3) xcex4 4.73 (4H, s), 2.15 (6H, s). 
Preparation 18. Dibenzyl methylthiomethyl phosphate
CH3SCH2OP(O)(OBu)2 
To a solution of bis(methylthiomethyl)ether (30 mg, 2.34 mmol) and molecular sieves (300 mg) in THF (100 ml) at room temperature was added dibenzyl phosphate (2.74 g, 9.85 mmol) followed by N-iodosuccinimide (608 mg, 2.71 mmol) and the solution was stirred for 4 h. The reaction mixture was then diluted with ethyl acetate and filtered through a pad of celite. The filtrate was treated with a 1:1 (v:v) solution of saturated aqueous sodium bicarbonate and 5% aqueous sodium thiosulfate. The colorless organic extract was then washed with brine, dried over sodium sulfate and concentrated in vacuo to provide 600 mg (69%) of the title compound:
1H NMR (300 MHz, CDCl3) xcex4 7.35 (1OH, s), 5.29 (2H, d, J=12.2 Hz), 5.08 (4H, dd, J=8.0, 1.0 Hz), 4.68 (2H, s), 2.10 (3H, s).